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I did not say that fossilised wood from that area had a 0.1% chance of being volcanic hot silica solution - I said that perhaps 0.1% of the fossil wood around the world had such an origin (that is a vastly different thing). I expressed some doubt still about the origin, but that does not relate to that 0.1% probability, that is merely a balance of probability issue.Lefty said:
Lefty said:
No, that is a misuse of probability - 0.1% around the field does not mean 0.1% in a particular area (it could be 100% in a particular area). For example, northern South Australia is far, far bigger but lacks any volcanics but has wood everywhere.
Sapphires are a completely different and unrelated issue - they form at high T and P at depth and are brought to surface in the volcanoes and have nothing to do with hot water - the wood obviously did not come from that depth but is a near-surface feature related to water, which might be hot water or it might not. Possibly the same rocks are associated with both, but the origins are totally unrelated otherwise.
fossickeract said:
It is not who you are but the strength of argument that is relevant - I am giving you the prevailing opinion of the majority of geologists, gleaned from reading many scores of papers on the topic (I have about 11 ring folders here in my office filled solely with photocopies on this topic, and am currently drafting up a paper on the topic for publication). The conclusions are based on isotope, fluid inclusion and X-Ray studies (things that tell us mineralogy and temperature of formation) involving reasearch on which many more (hundreds of researchers) made the conclusions fromn which these people draw their own conclusions, involving tens of millions of dollars of research expenditure and perhaps a hundred years or more of combined full-time research time over the last few dacades. Only about 4 of those papers consider a limited number of examples (Beechworth, Coolgardie, New England district) of examples related to hot magmatic water, and in all cases even those authors do not consider the rest of the volcanic wood around the world or Australia to have such an origin (obviously it is not only three instances, there would be a lot, but the proportion is small). One point of confusion seems to be that I think you are possibly confusing one moderately common form of origin (the second one) relating to these things requiring volcanics already formed some time ago to supply the silica as they weather by the action of ordinary cold rainwater, with a rare origin that actually requires hot water evolved from the volcanics to do it. We have all sorts of other clues (eg rhodonite cannot form at low temperature and is common in chalcedonic veins formed at higher temperatures. I know a large proportion of the geos working on this and closely related issues in Australia. So it is not some idea of mine versus an idea of Lefties, it is the view of 50 or more geologists at the absolute minimum (ie some wrote more than one of the papers), drawing on the work of hundreds of other geologists. I thought it was of interest to you to know the prevailing majority view ("current dogma") and have passed it on, but if not that is fine, and I did not realise that you guys were so wedded to your own impressions. As for the other thing re pyropholite - it is not a mineral, it is a popular name that is being used. Agate, jasper, chalcedony, chert, silcrete are in most cases all the same mineral or a combination of up to three - opal, microquartz and megaquartz. It is their atomic structure that makes them a mineral (or minerals), not the fact that they are laid down in layers of different thickness, colour and purity, which ios what makes them appear different to us (eg trace iron in jasper commonly makes it red, but it is still one or more of those three minerals). The trend is away from inventing a new name geologically in such cases, where something is not actually a different mineral species (although I have no problem with jewellers or enthusiasts using varietal names) - but corundum, sapphire and ruby are all one mineral, corundum (for example). They only differ in colour, and the amount of impurity required to give that colour is miniscule (sometimes it is not even an impurity - for example the diferent colours of green versus red versus blue precious opal is not related to any impurites - they can be all pure opal of identical composition (the different diameter spheres that comprise their structure cause a different amount of refraction as light passes through them - as in a rainbow), so you see them as being different colours. Anyway, I see there is not much point in this, so won't discuss it further.
And the reference you quoted is 1961 - (yes, I read it in the past). Science advances continuously. That is 55 years ago, more than half a century. Yes, they had colour television for a number of years by then in the USA (and B& W television in Australia for a full 5 years) and had recently invented the laser at that time (I remember that because I was starting high school at the time and read up on the ruby laser). There was no synchro-mesh in 4x4 gearboxes. The first moon landing was only 8 years later (I listened to it in an earth-floor hut in the Victorian Alps using a large battery - operated radio with a wire strung in a tree), and electronic calculators were rare and most of the public had never seen one - I managed to finally get one in London 9 years later - it cost about $800, was big and clunky and could only add, subtract, multiply and divide. I think that was around the time when they got the first satellite to successfully orbit the Earth . Electrostatic copiers were not invented (Xerox's selenium drum machine was a couple of years later, my father was involved - the only copiers were photographic with chemicals and developer sloshing around in them, and a single page cost a fortune (which had its effect on the exchange of scientific knowledge). They had also invented transistors - although vacuum tubes (valves) were still widely used. Mobile phones were not invented, and it would be decades before the internet and email was invented (so scientists had limited access to the work of others, they could read it in libraries when the latest paper issue arrived by snail-mail). DNA and most aspects of genetics had still to be deciphered (one of my family was involved in that, a crystallographer). The first integrated paper on plate tectonics was not published for a further 9 years, and the idea of tectonic plates and their movement was little more than a vague untested idea still in the minds of perhaps a dozen geologists (most scoffed at the idea) - I graduated in geology before that first paper came out. Atomic absorption spectroscopy was about to be invented and would finally let us analyse elements down to tens of parts per million (I routinely analyse to parts per trillion now, and I use electron microscopes and we can actually see individual atoms nowadays).
The instruments that we know use to do the studies I mentioned had not been invented - and isotopes were virtually unused in geology.
The "sound" specimens make is really not a criterion for interpreting origin or comparing minerals, Lefty. I'm not having a go at you, I am trying to put it all in perspective for you. I know it is difficult for a non-geologist or non-specialist geologist, the explosion in knowledge is so great now that just being a geologist can be quite irrelevant - one has to be working in a particular branch of geology (I wouldn't have a clue about many branches any more). I have not tried to pull rank or give my credentials (as I say, it is not who you are but the strength of the argument) but I would not wax lyrical on things that I don't know a lot about without saying so.
It is very time-consuming explaining geological concepts (the current majority view, not mine) and obviously not greatly appreciated, so I'll drop out now. Good luck with the prospecting.
The instruments that we know use to do the studies I mentioned had not been invented - and isotopes were virtually unused in geology.
The "sound" specimens make is really not a criterion for interpreting origin or comparing minerals, Lefty. I'm not having a go at you, I am trying to put it all in perspective for you. I know it is difficult for a non-geologist or non-specialist geologist, the explosion in knowledge is so great now that just being a geologist can be quite irrelevant - one has to be working in a particular branch of geology (I wouldn't have a clue about many branches any more). I have not tried to pull rank or give my credentials (as I say, it is not who you are but the strength of the argument) but I would not wax lyrical on things that I don't know a lot about without saying so.
It is very time-consuming explaining geological concepts (the current majority view, not mine) and obviously not greatly appreciated, so I'll drop out now. Good luck with the prospecting.
silver
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You blokes are all full of it ,..... great info I mean ,... it amazes a simple fella like me to see the insights and understanding you fellas have from all the learning and putting one and four and four together out in the field to come up with145(more than the sum of the product),
Love the way it makes you think about it all ,... real detectivity ! 8)
Love the way it makes you think about it all ,... real detectivity ! 8)
I meant to show you this before I go. About 2013? I was in a research unit in northern Siberia (Magadan) on the northern shore of the Sea of Okhotsk. This is a great region for silica minerals. I photographed the floor in one large room (left) and the top of a coffee table about 130 cm in diameter (right). Drool....
Lefty, this change in geological knowledge due to techniques we did not have in the past has shown as that many of our past assumptions have been simplistic. For example you see steam billowing from volcanoes and it seems reasonable to assume that it has come from the magma at depth, but often that is quite incorrect (although part of the water will have that origin). We now know that a lot of it is simply rainwater that the magma has heated up when it comes in contact with it as it approaches the surface. So in many cases the gold veins that we see in veins around volcanoes were dominantly formed from hot rain water.
So we now tend to divide things up - where did the heat come from, where do the metals come from, where does the water come from, where does the sulphur come from, where does the carbonate (to form calcite) come from? So in some cases we find that that in the case of an ore deposit clearly associated with a volcano, that the metal came from the magma, the sulphur from sea water, the carbonate from limestone and the water mainly from rainwater (with a little bit of water from the magma).
Now weather that now old and solid igneous rock at a much later date in a wet climate, and elements like silica can dissolve in the rain water and migrate away from the igneous rock into gravels etc to replace wood and form petrified wood.
However sapphires and rubies are different again - they crystallised as one of the first minerals to solidy in the magma and formed in it at depth on its way up - they have the same age approximately as the igneous rock, but have still been just "passengers" in the last part of its way to surface.
However most diamonds are different again, they formed three billion years ago at depth in the mantle (which is where magmas form billions of years later). They are entirely passengers that often have nothing to do with the manga, except that magma formed say 30 million years ago simply acts as a conveyor belt to bring those ancient diamonds to the surface.
This can make it difficult for an economic geologist to discuss with a non-geologist, because one is depending on evidence that cannot be "seen" visually, whereas the other is coming from the direction of making fairly simple assumptions (but often incorrect) assumptions of the type that geologists originally made in the past - e.g. "sapphires, rubies, petrified wood, diamonds, agate are spatially associated with volcanoes (i.e. commonly occur in their vicinity) and are therefore associated with volcanic processes and hot water produced from magmas. Bloody geos don't have a clue, it is obvious!" But in fact these minerals formed at three different times - long before the molten magma even existed, at the same time as the molten magma and long after the molten magma had long cooled (perhaps tens of millions of years after). The prospector says it is obvious because he and his mates always find these minerals near lavas and volcanic necks - the geologist is instead relying on a wealth of non-visual evidence derived by huge numbers of geologists.
Because in the case of silicified wood, the lava (in many cases) simply supplied silica to rainwater during weathering at a much later date, and because rocks other than lava can also supply silica in the same way as lava can during their weathering, silicified wood will in many cases occur in areas where there has never been lava.
Many geologists agree (for example) that in the case of Australian precious opal, the source of the silica was a clay (montmorillonite), that rainwater changes to another clay (kaolinite) during weathering, releasing silica in the process to form opal. Go to Coober Pedy and you will see the dark Bulldog Shale - this is a rock that consists of montmorillonite. However lying on top of the fresh Bulldog Shale (which you commonly only see fresh in the bottom of opal mines) you will see white weathered shale (partly altered to kaolinite), and above that pure white clay (kaolinite) that formed from the Bulldog Shale by rainwater during weathering. The opal never occurs more than a short distance into the top of fresh rock and is usually in weathered rock - it forms from silica released during the weathering of the rock and re-deposited in fractures in the weathered rock - never more than 10 m to 30 m below the original ground surface where rainwater could easily pentrate the rock.
Does it matter? Not if you are in a good area of volcanics and are finding stuff (I said in other posts how it is important to be in a basalt area to find sapphires, a granite area to form topaz). But the mistake would be to consider that things like agate and opal and jasper etc will be only found in those areas - some of the best fields for such minerals are nowhere near volcanic rocks. Also, even in volcanic areas the main control on where the petrified wood is, is where the original wood was - close proximity to a volcano is probably no guide at all to actual discovery, beyond telling you that you are in the right general region.
I guess that all sounds too complicated, but I have tried my best....;.
So we now tend to divide things up - where did the heat come from, where do the metals come from, where does the water come from, where does the sulphur come from, where does the carbonate (to form calcite) come from? So in some cases we find that that in the case of an ore deposit clearly associated with a volcano, that the metal came from the magma, the sulphur from sea water, the carbonate from limestone and the water mainly from rainwater (with a little bit of water from the magma).
Now weather that now old and solid igneous rock at a much later date in a wet climate, and elements like silica can dissolve in the rain water and migrate away from the igneous rock into gravels etc to replace wood and form petrified wood.
However sapphires and rubies are different again - they crystallised as one of the first minerals to solidy in the magma and formed in it at depth on its way up - they have the same age approximately as the igneous rock, but have still been just "passengers" in the last part of its way to surface.
However most diamonds are different again, they formed three billion years ago at depth in the mantle (which is where magmas form billions of years later). They are entirely passengers that often have nothing to do with the manga, except that magma formed say 30 million years ago simply acts as a conveyor belt to bring those ancient diamonds to the surface.
This can make it difficult for an economic geologist to discuss with a non-geologist, because one is depending on evidence that cannot be "seen" visually, whereas the other is coming from the direction of making fairly simple assumptions (but often incorrect) assumptions of the type that geologists originally made in the past - e.g. "sapphires, rubies, petrified wood, diamonds, agate are spatially associated with volcanoes (i.e. commonly occur in their vicinity) and are therefore associated with volcanic processes and hot water produced from magmas. Bloody geos don't have a clue, it is obvious!" But in fact these minerals formed at three different times - long before the molten magma even existed, at the same time as the molten magma and long after the molten magma had long cooled (perhaps tens of millions of years after). The prospector says it is obvious because he and his mates always find these minerals near lavas and volcanic necks - the geologist is instead relying on a wealth of non-visual evidence derived by huge numbers of geologists.
Because in the case of silicified wood, the lava (in many cases) simply supplied silica to rainwater during weathering at a much later date, and because rocks other than lava can also supply silica in the same way as lava can during their weathering, silicified wood will in many cases occur in areas where there has never been lava.
Many geologists agree (for example) that in the case of Australian precious opal, the source of the silica was a clay (montmorillonite), that rainwater changes to another clay (kaolinite) during weathering, releasing silica in the process to form opal. Go to Coober Pedy and you will see the dark Bulldog Shale - this is a rock that consists of montmorillonite. However lying on top of the fresh Bulldog Shale (which you commonly only see fresh in the bottom of opal mines) you will see white weathered shale (partly altered to kaolinite), and above that pure white clay (kaolinite) that formed from the Bulldog Shale by rainwater during weathering. The opal never occurs more than a short distance into the top of fresh rock and is usually in weathered rock - it forms from silica released during the weathering of the rock and re-deposited in fractures in the weathered rock - never more than 10 m to 30 m below the original ground surface where rainwater could easily pentrate the rock.
Does it matter? Not if you are in a good area of volcanics and are finding stuff (I said in other posts how it is important to be in a basalt area to find sapphires, a granite area to form topaz). But the mistake would be to consider that things like agate and opal and jasper etc will be only found in those areas - some of the best fields for such minerals are nowhere near volcanic rocks. Also, even in volcanic areas the main control on where the petrified wood is, is where the original wood was - close proximity to a volcano is probably no guide at all to actual discovery, beyond telling you that you are in the right general region.
I guess that all sounds too complicated, but I have tried my best....;.
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Cheers Goldirocks
The info you supply is good but you over-assume simplicity of observation I think. My opinion based on having been there and about the area many, many times remains unchanged - this particular wood and the local volcanics are intimately related. When you visit the site and spend a good amount of time around the area, you will conclude that it takes an extraordinary amount of faith to ignore all the factors I've already mentioned in favour of a broader theory. The wood in this area is always in conjunction with other volcanically-originated materials in the vicinity of volcanics (never seen sapphires there). All said materials cease to be present in the river gravel as you move upstream away from the field, including the wood. All said materials including the wood exist downstream of the site but seem to get progressively thinner and thinner as you keep moving downstream. Go far enough downstream and it becomes difficult to find any.
The wood is of no commercial value of course but if it was and I was mining it, I certainly wouldn't be saying to myself "well the books say one thing but the reality in front of me says another - reality must be wrong"
Again, not disagreeing with that, just pointing out that in the case of this region these materials seem virtually always found in the near vicinity of igneous rocks. And this region is rather large.
Here's another example. This seam agate (term approved by one with a geology degree ) type material is found in an area of badly decomposed granite near my home. Not super-exciting material but some of it cabs up nicely enough. The point is, where the deco granite ceases, so does this stuff. I've scoured the area but it is definitely confined to the igneous rock spot.
You keep saying that these materials are often unrelated to anything igneous. I'm not disputing that claim - what I'm saying is that it appears not to be the case here.
Out of interest, I'd like to see where these fields of abundant, high quality "cold agate" are since I am totally unfamiliar with such things. It will be good for to learn something new, I'm only familiar with stuff that I've only ever found associated with various kinds of hot rocks.
Cheers
The info you supply is good but you over-assume simplicity of observation I think. My opinion based on having been there and about the area many, many times remains unchanged - this particular wood and the local volcanics are intimately related. When you visit the site and spend a good amount of time around the area, you will conclude that it takes an extraordinary amount of faith to ignore all the factors I've already mentioned in favour of a broader theory. The wood in this area is always in conjunction with other volcanically-originated materials in the vicinity of volcanics (never seen sapphires there). All said materials cease to be present in the river gravel as you move upstream away from the field, including the wood. All said materials including the wood exist downstream of the site but seem to get progressively thinner and thinner as you keep moving downstream. Go far enough downstream and it becomes difficult to find any.
The wood is of no commercial value of course but if it was and I was mining it, I certainly wouldn't be saying to myself "well the books say one thing but the reality in front of me says another - reality must be wrong"
Again, not disagreeing with that, just pointing out that in the case of this region these materials seem virtually always found in the near vicinity of igneous rocks. And this region is rather large.
Here's another example. This seam agate (term approved by one with a geology degree
) type material is found in an area of badly decomposed granite near my home. Not super-exciting material but some of it cabs up nicely enough. The point is, where the deco granite ceases, so does this stuff. I've scoured the area but it is definitely confined to the igneous rock spot.
You keep saying that these materials are often unrelated to anything igneous. I'm not disputing that claim - what I'm saying is that it appears not to be the case here.
Out of interest, I'd like to see where these fields of abundant, high quality "cold agate" are since I am totally unfamiliar with such things. It will be good for to learn something new, I'm only familiar with stuff that I've only ever found associated with various kinds of hot rocks.
Cheers
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Oh, I'm not saying it is - it's just an observation.
I'm sure you're not saying that we should ignore basic sensory info - I would have thought that to be the sign of a rather poor field operative.
All I've noted is that the pet wood from Riverslea volcanic area is often glossy and glazed-looking, extremely hard and makes an unusual, sharp sound when struck together, similar to clacking two glass marbles together.
This contrasts markedly to the few bits I've found that come from areas apparently devoid of volcanics which are dull in surface lustre, of a somewhat porous appearance and which make a duller-sounding thud.
Why the two are different in this respect is probably a matter for conjecture - but it doesn't seem unreasonable to me assume that somewhat different petrification processes may have been involved. Perhaps the porous specimen formed more slowly at lower temperature, allowing biological decay agents to partially consume it before it could become too silicified for them to keep decomposing, leading to a porous-textured fossil wood.
Conversely, perhaps the Riverslea specimens were silicified more quickly under conditions hostile to living organisms - let's say, very hot silica solution from volcanics, leading to a fossil wood with a dense, non-porous, hard glassy structure.
The above is just conjecture of course, could all be completely wrong. But whatever the books may or may not say, the two are quite distinct to the eye, to the ear and to the touch.
Just a first-hand observation, nothing more.
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Not far at all from Riversla is Mount Hay, home to this sort of stuff
You see what I'm saying? I'm not saying that cold-formed agates/chalcedonies may not be very common elsewhere, I'm saying that in the part of Australia I live in, virtually every example of such material I can think of offhand is definitely igneous.
There are no thundereggs or "rainforest jasper" as they term it for sale at Riverslea, Mount Hay is downstream. But it's very close and again I note how two different volcanoes in very close proximity to each other can have produced quite different things.
Interesting stuff.
You see what I'm saying? I'm not saying that cold-formed agates/chalcedonies may not be very common elsewhere, I'm saying that in the part of Australia I live in, virtually every example of such material I can think of offhand is definitely igneous.
There are no thundereggs or "rainforest jasper" as they term it for sale at Riverslea, Mount Hay is downstream. But it's very close and again I note how two different volcanoes in very close proximity to each other can have produced quite different things.
Interesting stuff.
I realize that geology is not always an exact science as quiet a bit of it involves theory. Again, i am no expert, just a first year geo student trying to understand as much as i can. That is the way we learn after all.
But i must say some of what you say goldierocks does seem to go against what i learned in first year. This does not mean you are wrong, again i am just trying to understand what you are describing.
I understand the principles of chemical and physical weathering, but again my understanding is that we have so much quartz sand present because quartz does get broken down by physical weathering into small grains, but that most siliceous material besides amorphous SiO2 was quiet resistant to chemical weathering, or it does not easily dissolve into cooler waters. Again my understanding is that you need a minimum of 100 C and extreme pressure to start dissolving most SiO2, which i believe would have been the case at the opal fields as they are at a depth not on the surface?
This is where you loose me when you talk about rainwater dissolving SiO2, again yes amorphous SiO2 would be dissolved to a point but the bulk of SiO2 is not amorphous to my understanding as it needs to undergo an acidification process?
Thank you again for sharing your knowledge, please do not take any offence by people questioning what you say, again that is how we all learn.
But i must say some of what you say goldierocks does seem to go against what i learned in first year. This does not mean you are wrong, again i am just trying to understand what you are describing.
I understand the principles of chemical and physical weathering, but again my understanding is that we have so much quartz sand present because quartz does get broken down by physical weathering into small grains, but that most siliceous material besides amorphous SiO2 was quiet resistant to chemical weathering, or it does not easily dissolve into cooler waters. Again my understanding is that you need a minimum of 100 C and extreme pressure to start dissolving most SiO2, which i believe would have been the case at the opal fields as they are at a depth not on the surface?
This is where you loose me when you talk about rainwater dissolving SiO2, again yes amorphous SiO2 would be dissolved to a point but the bulk of SiO2 is not amorphous to my understanding as it needs to undergo an acidification process?
Thank you again for sharing your knowledge, please do not take any offence by people questioning what you say, again that is how we all learn.
Lefty, I don't have the time to explain (not that I would not like to, it is simply time, not being offended or anything - I said I would drop out, but that was because I did not think we could ever get anywhere - that you were not appreciating my meaning). Firstly, because basically you are saying that I have said things that I have not said (talking about different minerals) and secondly there is confusion in the scientific versus non-scientific use of words. For example, I say something about one mineral, and you read it as also being said about another - and then disagree with what I have not actually said . You think I am disagreeing with far more than what I am disagreeing with. I am using a geological definition of igneous origin you are using a spatial defintion (that they occur together), so what I say is quite true in terms of my terms of reference (a very rigid and tightly-defined scientific one), what you say is quite true in terms of yours (a spatial one). So I will confine my answer to principles.
Likewise, the many examples of what you consider different minerals are not different "minerals" they are different "mineral varieties" of a single mineral. For example, agate or chalcedony or in many cases jasper are mineral varieties of the mineral quartz (which in this case is fine-grained so we call it microquartz, which is itself just a variety of the mineral quartz - a change in gransize does not turn it into a different mineral any more than being red, white or yellow does, or being banded does - jasper is usually simply the red mineral variety of the mineral quartz which is fine-grained). Geologists get sick of saying "mineral variety", so will often just say "mineral" as short-hand, thus confusing the understanding of you poor buggers completely. To complicate it further, many mineral collectors talk of rocks as minerals - chert is a rock (not a mineral) usually composed of chalcedony which is one fine-grained mineral variety of quartz, silcrete is a rock composed of chalcedony which is also a fine-grained mineral variety of the mineral quartz, and some geologists use jasper as a rock name not a mineral species name. They are called rocks because they comprise huge volumes of the same material (if you have a silcrete layer a metre thick over ten thousand sq km it sounds a bit strange to talk about it as a mineral layer - it is a mono-mineralic rock later - see photo). We give the rocks different names for the same reason we give different names to mineral varieties despite them being one mineral - because silcrete and chert LOOK different to us, but they are both quartz rocks. Collectors confuse the issue further by inventing names that they consider mineral names for things that are not minerals at all in a scientific sense, but rocks composed of mixtures of minerals (eg the one discussed from Pambula which is a mixture of illite and volcanic glass) - I'm guessing 75% of NSW collectors but only perhaps 5% of geologists worldwide would have ever heard that name - I only knew it because I mapped in the Nethercote quarry where it occurred. Even geologists (professional mineralogists) sometimes initially make errors (heaven forbid!) - I was given an award of polished selwynite, which geologists originally thought was a purplish mineral - it is now known to be not a mineral, but a rock that is a mixture of minerals, but if you Google it you will find almost every site calls it a mineral - it is so entrenched that it is impossible to get rid of this misuse by even some mineralogists who only refer to the early descriptions and don't know it is now a "discredited mineral".
You are not wrong to do this, and I am not wrong, I use the language of science but you use the language of collectors - it is convenient for you, you know exactly what you are talking about when you use the term with each other (which is EXACTLY the same reason scientists use the scientific term with each other). The scientific term nevertheless has the advantage of being EXACTLY defined, so there is no ambiguity (yes it might be called red chalcedony, yes it might be jasper, yes it might be called red chert - but in every case it is definitely a red, fine-grained variety of the mineral quartz). Government brochures etc (I write some of them, and others quote in them what I write elsewhere) will often use the collectors term to make it easy for them to read - if I said "a devitrified sericitised rhyolite" many collectors would scratch their heads and say "what the hell does this pamphlet have to do with fossicking for gems!""why the hell didn't he say pyro..... then!")
There are all sorts of assumptions as well in this discussion that are quite incorrect, and it would take a long time to address each one. For example, the assumption that silica cannot dissolve at low temperature - large volumes can dissolve at no more than a couple of degrees Celsius, huge volumes of chalcedony form at temperatures no hotter than an Australian midday, and form fairly continously over areas of hundreds of thousands of square km in fairly pure layers up to many metres thick, some of it worth slabbing, and most occurs in areas with no igneous rocks. Also:
"most siliceous material besides amorphous SiO2 was quite resistant to chemical weathering, or it does not easily dissolve into cooler waters". Definitely not so, ask if you want a fuller explanation.
"you need a minimum of 100 C and extreme pressure to start dissolving most SiO2" - absolutely incorrect - again ask if you want (I have time to answer very specific questions, but a lot of the above has been going around in circles with things where there is little or no disagreement and that gets us nowhere (eg the idea that agate can often be igneous in origin - sure it can be - not at all uncommon)
"the case at the opal fields as they are at a depth not on the surface?" no, as I described in detail previously the opals are within 30 m of the surface when they form, not at depth, within the zone where lots of water can penetrate, although some rainwater can go to km depth in small quantities. The deepest opal mine shaft in Australia is probably only 45 m, and is only that deep because a layer of gravel and silcrete was added on top after the opal formed.
"this is where you lose me when you talk about rainwater dissolving SiO2, again yes amorphous SiO2 would be dissolved to a point but the bulk of SiO2 is not amorphous" [which I take it means you are implying that it therefore would not dissolve]. No, this is also quite incorrect, but through misunderstanding of what I am discussing when I say silica (which I can fully understand)
Geochemists such as myself talk about dissolving "the silica" from a mineral, I am not talking about dissolving a mineral that is pure SiO2, I am talking about releasing the SiO2 (silica) component of a more complex mineral, such as olivine, pyroxene, plagioclase (eg labradorite). By the way, labradorite is plagioclase but it is reasonable to call labradorite a mineral (not a mineral variety) because we say that plagioclase is a mineral of varying composition (a "solid solution series", ranging from albite Na Al silicate to labradorite Ca Al silicate), so each range of composition in that mineral series can be called by an individual mineral name - albite, oligoclase, andesine, labradorite, bytownite, anorthite (although geologists are trying to do away with this and just say "plagioclase An30"- so albite is 90% Na, 10% Ca and at the other end anorthite is 90% Ca 10% Na - plagioclase is a mineral of varying composition and we simply make arbitary divisions at 10%, 30%, 50% etc.... Your heads must be spinning.....
To explain "silica", e.g. take Mg2Si04 (in an igneous rock) + (add) CO2 (from the atmosphere or dissolved in groundwater) = (gives) Mg(CO3) + SiO2 (which is dissolved in groundwater; I have not bothered to balance the equation). I have thus released the silica from the mineral olivine, and that released silica has dissolved in groundwater, and what remains is now the mineral magnesite. Olivine is actually very unstable at surface and this occurs readily. The dissolved silica can now travel in that rainwater through the rocks (we now call it groundwater) and when it encounters fragments of wood (usually in tuff or gravel etc because the majority of wood in molten lava burns away - not all)) it can precipitate and replace the wood, giving petrified wood. Similarly other things occur - feldspar (such as plagioclase - a Ca Al silicate) reacts with water to give hydrous Al silicate, such as the clay mineral kaolinite (there is a different amount of silica in this c.f. with the original felspar) and releases part of the silica plus the Ca into groundwater. Plagioclase is also fairly unstable at surface so this occurs fairly readily (a bit less rapidly than with the olivine). The olivine can also react with water to give Mg(OH)2 brucite, releasing all its silica. So an olivine-plagioclase rock (eg basalt) that formed 30 My ago can be temprarily protected from weathering for millions of years by later overlying rocks, but at say 4 My can weather to a magnesite-brucite-kaolinite rock and release lots of silica which can dissolve in water at a temperature of say 15 degrees C and move into a gravel or tuff that formed at 5 My (or 60 My if you prefer) and react with wood in it to form petrified wood. I would say - "the petrified wood does not have an igneous origin, because it originated 26 My years after the basalt formed, from wood perhaps deposited 1 My earlier than the petrification - at a time after the lava coolled completely and started to be weathered". Lefty might say "it is in tuff which is a volcanic rock which is igneous so the bloody thing has an igneous origin". I would say, no, it didn't originate then, it originated 25 My later (its genesis was 25 My later), so we cannot possibly say its origin (genesis) is igneous - the two things (tuff and petrified wood) originated at vastly different times. Do you see why I say we are going around in circles?
The same is true with opals and the Bulldog Shale - its silica rich Ca clay (montmorillonite), weathers near surface to a silica-poor clay (kaolinite) and some silica and all the Ca are released - the silica precipitates in fractures as opal at perhaps 10 m or 15 m greater depth as the silica-rich water travels down to the water-table, and the Ca probably reacts with CO2 in the water to give us calcite veins.
Consider formation of jasper. Olivine, like plagioclase, is also a solid solution series that ranges from Mg2Si04 (forsterite) to Fe2SiO4 (fayalite) and most olivine falls somewhere in between (there are a series of intermediate names like hortonolite etc). So take olivine that is (Fe,Mg)2Si04 + CO2 (from the atmosphere, or dissolved in cold groundwater) - this gives Mg(CO3) + SiO2 + Fe (the last two being dissolved in groundwater, the magnesite staying behind). The Si02 and Fe move away in the water and something causes them to precipitate together (there can be various causes) - as they precipitate together, microscopic particles of red Fe203 (hematite) are intimately caught up in the white fine-grained quartz, giving the resulting rock mixture (which is jasper) a red colour.
I would like to give you references on some of these things, but I value anonymity and would lose that to give you some papers I have published on exactly these topics (including opals, silcretes etc). I have a great dislike of people "pulling rank", using things like their qualifications rather than the quality of their arguments to win points (not that many professors don't talk a bit of b.s. at times), and I try very hard not to do so (pull rank). However it puts me at a disadvantage when I have written some of the stuff on this topic but want to remain anonymous. So to just put it in context (just in terms of the relevance of you quoting what you learnt in first year to question my arguments, not as a put-down), I am a "professor" with a PhD and nearly 50 years since graduation in geology and geochemistry and experience in scores of countries on 5 continents, 12 years of it outside Australia, as a university lecturer at undergrad and postgraduate level, and a former CSIRO scientist who does research on, publishes on, and supervises postgraduate degrees on things like silcrete, opal, chert and also high-temperature chalcedony etc. (in various countries). I only mention this to make clear that I do tend to be sure of my facts in terms of processes etc (although I can be as wrong as anyone else in a specific case, and have been known to sprout pure b.s after too many beers). But I am careful in what I say - if I only "think" something or "tend to disagree", or "estimate" something I try to say so and you can read that as personal opinions based on a lot of experience but that could be wrong. If I state something definitely I am trying to tell you things based on the majority view att his time of scientists working on that topic - the general consensus of experts AT THIS POINT IN TIME (called "current scientific dogma"). Even that changes with time in the scientific community and any scientist who claims absolute proof of an idea is not a good scientist - we "work towards towards the truth". We can talk of postulates, hypotheses and theories which are used for our increasing degrees of confidence that we are approaching the truth. Although we do disagree on SOME things all the time. we are often unfairly criticised for not agreeing with each other on major issues by people who ignore the fact that one person was writing in 1962 and another in 2012. However, although ideas do change with time, it is quite rare for a full reversal in ideas to occur (it has been known) - the tendency is more towards a better degree of understanding while still not having absolute knowledge.
We are an easy target because we admit to our uncertainties (climate change is one such area where that is used against scientists - the non-scientist say "it is bloody obvious that this year is colder not hotter than last year in Melbourne" and the scientist says "our best estimate at this time is that the rolling mean of temperatures over the the last ten years shows fairly convincingly that there has been a steady increase in temperature of the atmosphere as a whole (globally) over that time" - "bloody scientists, non-committal, talk about "best estimates", say "fairly convincingly", only see it if they average things, don't even explain my comment on Melbourne:" (ignoring of course that it is GLOBAL warming being talked about, not the temperature of Melbourne - some areas go down a bit over a few years, some go up a bit over those years, but the global average over those years is the average of a huge number of localities, not of one or a few places). It is difficult to explain the complexity of science to a non-scientist, because it simply requires the non-scientist to learn so much science before some understanduing comes. But intelligent people like you guys try to learn some, and that is good, since you do understand what you do better as a result.
Likewise, the many examples of what you consider different minerals are not different "minerals" they are different "mineral varieties" of a single mineral. For example, agate or chalcedony or in many cases jasper are mineral varieties of the mineral quartz (which in this case is fine-grained so we call it microquartz, which is itself just a variety of the mineral quartz - a change in gransize does not turn it into a different mineral any more than being red, white or yellow does, or being banded does - jasper is usually simply the red mineral variety of the mineral quartz which is fine-grained). Geologists get sick of saying "mineral variety", so will often just say "mineral" as short-hand, thus confusing the understanding of you poor buggers completely. To complicate it further, many mineral collectors talk of rocks as minerals - chert is a rock (not a mineral) usually composed of chalcedony which is one fine-grained mineral variety of quartz, silcrete is a rock composed of chalcedony which is also a fine-grained mineral variety of the mineral quartz, and some geologists use jasper as a rock name not a mineral species name. They are called rocks because they comprise huge volumes of the same material (if you have a silcrete layer a metre thick over ten thousand sq km it sounds a bit strange to talk about it as a mineral layer - it is a mono-mineralic rock later - see photo). We give the rocks different names for the same reason we give different names to mineral varieties despite them being one mineral - because silcrete and chert LOOK different to us, but they are both quartz rocks. Collectors confuse the issue further by inventing names that they consider mineral names for things that are not minerals at all in a scientific sense, but rocks composed of mixtures of minerals (eg the one discussed from Pambula which is a mixture of illite and volcanic glass) - I'm guessing 75% of NSW collectors but only perhaps 5% of geologists worldwide would have ever heard that name - I only knew it because I mapped in the Nethercote quarry where it occurred. Even geologists (professional mineralogists) sometimes initially make errors (heaven forbid!) - I was given an award of polished selwynite, which geologists originally thought was a purplish mineral - it is now known to be not a mineral, but a rock that is a mixture of minerals, but if you Google it you will find almost every site calls it a mineral - it is so entrenched that it is impossible to get rid of this misuse by even some mineralogists who only refer to the early descriptions and don't know it is now a "discredited mineral".
You are not wrong to do this, and I am not wrong, I use the language of science but you use the language of collectors - it is convenient for you, you know exactly what you are talking about when you use the term with each other (which is EXACTLY the same reason scientists use the scientific term with each other). The scientific term nevertheless has the advantage of being EXACTLY defined, so there is no ambiguity (yes it might be called red chalcedony, yes it might be jasper, yes it might be called red chert - but in every case it is definitely a red, fine-grained variety of the mineral quartz). Government brochures etc (I write some of them, and others quote in them what I write elsewhere) will often use the collectors term to make it easy for them to read - if I said "a devitrified sericitised rhyolite" many collectors would scratch their heads and say "what the hell does this pamphlet have to do with fossicking for gems!""why the hell didn't he say pyro..... then!")
There are all sorts of assumptions as well in this discussion that are quite incorrect, and it would take a long time to address each one. For example, the assumption that silica cannot dissolve at low temperature - large volumes can dissolve at no more than a couple of degrees Celsius, huge volumes of chalcedony form at temperatures no hotter than an Australian midday, and form fairly continously over areas of hundreds of thousands of square km in fairly pure layers up to many metres thick, some of it worth slabbing, and most occurs in areas with no igneous rocks. Also:
"most siliceous material besides amorphous SiO2 was quite resistant to chemical weathering, or it does not easily dissolve into cooler waters". Definitely not so, ask if you want a fuller explanation.
"you need a minimum of 100 C and extreme pressure to start dissolving most SiO2" - absolutely incorrect - again ask if you want (I have time to answer very specific questions, but a lot of the above has been going around in circles with things where there is little or no disagreement and that gets us nowhere (eg the idea that agate can often be igneous in origin - sure it can be - not at all uncommon)
"the case at the opal fields as they are at a depth not on the surface?" no, as I described in detail previously the opals are within 30 m of the surface when they form, not at depth, within the zone where lots of water can penetrate, although some rainwater can go to km depth in small quantities. The deepest opal mine shaft in Australia is probably only 45 m, and is only that deep because a layer of gravel and silcrete was added on top after the opal formed.
"this is where you lose me when you talk about rainwater dissolving SiO2, again yes amorphous SiO2 would be dissolved to a point but the bulk of SiO2 is not amorphous" [which I take it means you are implying that it therefore would not dissolve]. No, this is also quite incorrect, but through misunderstanding of what I am discussing when I say silica (which I can fully understand)
Geochemists such as myself talk about dissolving "the silica" from a mineral, I am not talking about dissolving a mineral that is pure SiO2, I am talking about releasing the SiO2 (silica) component of a more complex mineral, such as olivine, pyroxene, plagioclase (eg labradorite). By the way, labradorite is plagioclase but it is reasonable to call labradorite a mineral (not a mineral variety) because we say that plagioclase is a mineral of varying composition (a "solid solution series", ranging from albite Na Al silicate to labradorite Ca Al silicate), so each range of composition in that mineral series can be called by an individual mineral name - albite, oligoclase, andesine, labradorite, bytownite, anorthite (although geologists are trying to do away with this and just say "plagioclase An30"- so albite is 90% Na, 10% Ca and at the other end anorthite is 90% Ca 10% Na - plagioclase is a mineral of varying composition and we simply make arbitary divisions at 10%, 30%, 50% etc.... Your heads must be spinning.....
To explain "silica", e.g. take Mg2Si04 (in an igneous rock) + (add) CO2 (from the atmosphere or dissolved in groundwater) = (gives) Mg(CO3) + SiO2 (which is dissolved in groundwater; I have not bothered to balance the equation). I have thus released the silica from the mineral olivine, and that released silica has dissolved in groundwater, and what remains is now the mineral magnesite. Olivine is actually very unstable at surface and this occurs readily. The dissolved silica can now travel in that rainwater through the rocks (we now call it groundwater) and when it encounters fragments of wood (usually in tuff or gravel etc because the majority of wood in molten lava burns away - not all)) it can precipitate and replace the wood, giving petrified wood. Similarly other things occur - feldspar (such as plagioclase - a Ca Al silicate) reacts with water to give hydrous Al silicate, such as the clay mineral kaolinite (there is a different amount of silica in this c.f. with the original felspar) and releases part of the silica plus the Ca into groundwater. Plagioclase is also fairly unstable at surface so this occurs fairly readily (a bit less rapidly than with the olivine). The olivine can also react with water to give Mg(OH)2 brucite, releasing all its silica. So an olivine-plagioclase rock (eg basalt) that formed 30 My ago can be temprarily protected from weathering for millions of years by later overlying rocks, but at say 4 My can weather to a magnesite-brucite-kaolinite rock and release lots of silica which can dissolve in water at a temperature of say 15 degrees C and move into a gravel or tuff that formed at 5 My (or 60 My if you prefer) and react with wood in it to form petrified wood. I would say - "the petrified wood does not have an igneous origin, because it originated 26 My years after the basalt formed, from wood perhaps deposited 1 My earlier than the petrification - at a time after the lava coolled completely and started to be weathered". Lefty might say "it is in tuff which is a volcanic rock which is igneous so the bloody thing has an igneous origin". I would say, no, it didn't originate then, it originated 25 My later (its genesis was 25 My later), so we cannot possibly say its origin (genesis) is igneous - the two things (tuff and petrified wood) originated at vastly different times. Do you see why I say we are going around in circles?
The same is true with opals and the Bulldog Shale - its silica rich Ca clay (montmorillonite), weathers near surface to a silica-poor clay (kaolinite) and some silica and all the Ca are released - the silica precipitates in fractures as opal at perhaps 10 m or 15 m greater depth as the silica-rich water travels down to the water-table, and the Ca probably reacts with CO2 in the water to give us calcite veins.
Consider formation of jasper. Olivine, like plagioclase, is also a solid solution series that ranges from Mg2Si04 (forsterite) to Fe2SiO4 (fayalite) and most olivine falls somewhere in between (there are a series of intermediate names like hortonolite etc). So take olivine that is (Fe,Mg)2Si04 + CO2 (from the atmosphere, or dissolved in cold groundwater) - this gives Mg(CO3) + SiO2 + Fe (the last two being dissolved in groundwater, the magnesite staying behind). The Si02 and Fe move away in the water and something causes them to precipitate together (there can be various causes) - as they precipitate together, microscopic particles of red Fe203 (hematite) are intimately caught up in the white fine-grained quartz, giving the resulting rock mixture (which is jasper) a red colour.
I would like to give you references on some of these things, but I value anonymity and would lose that to give you some papers I have published on exactly these topics (including opals, silcretes etc). I have a great dislike of people "pulling rank", using things like their qualifications rather than the quality of their arguments to win points (not that many professors don't talk a bit of b.s. at times), and I try very hard not to do so (pull rank). However it puts me at a disadvantage when I have written some of the stuff on this topic but want to remain anonymous. So to just put it in context (just in terms of the relevance of you quoting what you learnt in first year to question my arguments, not as a put-down), I am a "professor" with a PhD and nearly 50 years since graduation in geology and geochemistry and experience in scores of countries on 5 continents, 12 years of it outside Australia, as a university lecturer at undergrad and postgraduate level, and a former CSIRO scientist who does research on, publishes on, and supervises postgraduate degrees on things like silcrete, opal, chert and also high-temperature chalcedony etc. (in various countries). I only mention this to make clear that I do tend to be sure of my facts in terms of processes etc (although I can be as wrong as anyone else in a specific case, and have been known to sprout pure b.s after too many beers). But I am careful in what I say - if I only "think" something or "tend to disagree", or "estimate" something I try to say so and you can read that as personal opinions based on a lot of experience but that could be wrong. If I state something definitely I am trying to tell you things based on the majority view att his time of scientists working on that topic - the general consensus of experts AT THIS POINT IN TIME (called "current scientific dogma"). Even that changes with time in the scientific community and any scientist who claims absolute proof of an idea is not a good scientist - we "work towards towards the truth". We can talk of postulates, hypotheses and theories which are used for our increasing degrees of confidence that we are approaching the truth. Although we do disagree on SOME things all the time. we are often unfairly criticised for not agreeing with each other on major issues by people who ignore the fact that one person was writing in 1962 and another in 2012. However, although ideas do change with time, it is quite rare for a full reversal in ideas to occur (it has been known) - the tendency is more towards a better degree of understanding while still not having absolute knowledge.
We are an easy target because we admit to our uncertainties (climate change is one such area where that is used against scientists - the non-scientist say "it is bloody obvious that this year is colder not hotter than last year in Melbourne" and the scientist says "our best estimate at this time is that the rolling mean of temperatures over the the last ten years shows fairly convincingly that there has been a steady increase in temperature of the atmosphere as a whole (globally) over that time" - "bloody scientists, non-committal, talk about "best estimates", say "fairly convincingly", only see it if they average things, don't even explain my comment on Melbourne:" (ignoring of course that it is GLOBAL warming being talked about, not the temperature of Melbourne - some areas go down a bit over a few years, some go up a bit over those years, but the global average over those years is the average of a huge number of localities, not of one or a few places). It is difficult to explain the complexity of science to a non-scientist, because it simply requires the non-scientist to learn so much science before some understanduing comes. But intelligent people like you guys try to learn some, and that is good, since you do understand what you do better as a result.
silver
silver
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All I can say is wow, and professor goldierocks you may need to start your own parralell threads to discuss some matters as being all scientific brings with it a certain charismatic charm coupled with a strong personality ,... at least that way the threads will be your little babies and fellow members will be able to discuss the aspects of geology in a mood of unfettered authority with respect to your geological prowess, which I may say is obviously extensive ,... as you have a lot to say and we all do like to listen it will be a boon for PA to be able to reflect upon and call upon the issue of your greymatter.
respectfully
Silver.
respectfully
Silver.
First off i would like to thank you again for taking the time to explain yourself in the depths you have. As i was trying to get at before, for me understanding comes better with discussion and unfortunately as i am so far from the UNI i study at, i do not get the opportunity to discuss geology very much and so for me the last couple of days have been very stimulating, though difficult when done on the forum due to what i believe have been minor misunderstandings.
Also please do not think i was pulling rank talking about being a 1st year student, i was trying to explain where my interest was and why i only have a very limited understanding. Maybe i could puff my chest a bit more if i had my diploma but a year one student is nothing to boast about This is also why i try to say "it is my understanding" not "this is how it is", but at the same time i guess i do like to think i have a basic understanding of some things and have not being wasting my time, hence trying to clear up what i was not understanding.
For me the confusion started when you said:
With the talk of volcanics being absent i did not consider weathering basalt, but did consider feldspars, but this is where from my limited understanding of chemistry i did not think the silica could be absorbed by the water readily because of temperature and this is why i kept asking about silica dissolving in cooler water. Not because i was saying you were wrong, but because it did go against what i thought i had learnt.
It seemed very drilled in to us at UNI, that around volcanoes and magma chambers any groundwater and water expelled from the magma usually got super heated and was more easily able to dissolve minerals from the rock it was passing through, most commonly silica creating a supersaturated solution. I think i understand about chalcedony/agate and opal precipitating out in cooler temps than quartz, but because of what we were taught, i guess i just associated the actual dissolving of the silica in most cases to magma/lava and the subduction of oceanic crust under continental crust.
What little i do know about geology is mostly theoretical, i have got to spend a little time in the New England area with the UNI studying and mapping ( this is where i saw fossil plants and wood preserved in carbonate rich mud and sandstone), but that is the limit of my field experience. To try and further my understanding i have been trying to learn and understand the local geology a little better and this is where my interest in the petrified wood and how it formed started. One of the reasons i had assumed volcanics had had something to do with the process was because some of the jasper found there seems to have been formed from altered conglomerate and sandstone hundreds of meters below where the flow sits today and the jasper seemed to have an association with at least some of the wood found.
Also as fossickeract said, the closer to the origin of the flow the more burnt the wood seems to be, which led me to think that if the wood was close enough to the surface to be burnt by lava or ash, then the surrounding ground water would also have been effected, which may have had something to do with the altered conglomerate and sandstone?
I could be way off the mark (as i have said my understanding is very limited) and would be happy to find out i am wrong so i can hopefully start looking in the right direction.
Age of the wood and different layers is only something i had recently started taking into consideration, so far i have not been able to find much information on the age of the wood and there has been very limited geological studies done on our area so a lot of the information is dated, though what i have found and been shown has been a great help.
Again thank you for your contribution everyone.
Also please do not think i was pulling rank talking about being a 1st year student, i was trying to explain where my interest was and why i only have a very limited understanding. Maybe i could puff my chest a bit more if i had my diploma but a year one student is nothing to boast about
This is also why i try to say "it is my understanding" not "this is how it is", but at the same time i guess i do like to think i have a basic understanding of some things and have not being wasting my time, hence trying to clear up what i was not understanding.For me the confusion started when you said:
The first thing i thought about was quartz rich sand and pebbles in the gravels you talk about, which in most (but not all) instances would be the case and i assumed you were saying the ground water was dissolving and distributing this silica. This was an assumption on my part.
With the talk of volcanics being absent i did not consider weathering basalt, but did consider feldspars, but this is where from my limited understanding of chemistry i did not think the silica could be absorbed by the water readily because of temperature and this is why i kept asking about silica dissolving in cooler water. Not because i was saying you were wrong, but because it did go against what i thought i had learnt.
It seemed very drilled in to us at UNI, that around volcanoes and magma chambers any groundwater and water expelled from the magma usually got super heated and was more easily able to dissolve minerals from the rock it was passing through, most commonly silica creating a supersaturated solution. I think i understand about chalcedony/agate and opal precipitating out in cooler temps than quartz, but because of what we were taught, i guess i just associated the actual dissolving of the silica in most cases to magma/lava and the subduction of oceanic crust under continental crust.
What little i do know about geology is mostly theoretical, i have got to spend a little time in the New England area with the UNI studying and mapping ( this is where i saw fossil plants and wood preserved in carbonate rich mud and sandstone), but that is the limit of my field experience. To try and further my understanding i have been trying to learn and understand the local geology a little better and this is where my interest in the petrified wood and how it formed started. One of the reasons i had assumed volcanics had had something to do with the process was because some of the jasper found there seems to have been formed from altered conglomerate and sandstone hundreds of meters below where the flow sits today and the jasper seemed to have an association with at least some of the wood found.
Also as fossickeract said, the closer to the origin of the flow the more burnt the wood seems to be, which led me to think that if the wood was close enough to the surface to be burnt by lava or ash, then the surrounding ground water would also have been effected, which may have had something to do with the altered conglomerate and sandstone?
I could be way off the mark (as i have said my understanding is very limited) and would be happy to find out i am wrong so i can hopefully start looking in the right direction.
Age of the wood and different layers is only something i had recently started taking into consideration, so far i have not been able to find much information on the age of the wood and there has been very limited geological studies done on our area so a lot of the information is dated, though what i have found and been shown has been a great help.
Again thank you for your contribution everyone.
Good luck with the studies Shivan. The problem with getting one key issue incorrect is that it can colour everything else (eg that silica can't be dissolved and precipitated at low temperature). Many other things you say are quite correct, such as your comments about magmas - but one thing to keep in mind is that a lot of that hot water hasn't come from the magma, but is simply groundwater (originally rainwater) that gets heated by the hot magma being injected into it - the geysers you see in NZ are essentially of that type. Clues to high temperature origins are usually minerals that can't form at low temperature, like rhodonite (a Mn pyroxene that only forms well above 200 degrees), hydrothermal (not magmatic) K felspars like adularia, native S when near an intrusion, sulphide minerals other than Fe sulphides. If you see them closely associated with what you are looking at there has probably been hot water around. They usually leave lots of evidence - this photo I took in the throat of the White Island volcano shows that - the haze in the air is native sulphur, which is why we are wearing gas masks (poisonous).
