Beginners Detecting Mistake..."Walking away from gold too soon."

Prospecting Australia

Help Support Prospecting Australia:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

WalnLiz

In remembrance, April 2024
Joined
Jan 20, 2013
Messages
3,931
Reaction score
4,204
Location
Australia, NSW
One thing I have noticed with some friends who tag along with us on detecting trips is that they find a piece of gold, quickly go over the area, and then walk on far too soon in an attempt to cover as much ground as they can. When detecting in creek beds gold rarely deposits in singular pieces, so if you find a piece, the chances of more being very close is extremely high. Gold is a very communal metal that likes hanging around with its mates.;) Most know the saying "Go low and go slow" but not enough beginners know that you "don't leave gold to find gold". If you find a couple of pieces in close proximity on say an inside creek bend, or bench, and hear no more obvious targets, don't just walk off thinking you have got it all. A small amount of "surfacing" by taking ten centimetres off the surface can very often expose "nests" of small nuggets just outside the reach of what you have already detected. We do this when chasing Reef gold, but not enough new to the game do this when hunting alluvial as well, instead they ping a small nugget and walk away too soon, hastily chasing the next piece.

Snapshot_2943.png Snapshot_2942.png
Something as simple as removing the grass from around a detected nugget, can often dramatically increase the total number of your finds. In this instance, we converted 4 small nuggets into 28... Most would have walked away and been happy with just the four.

A very clear case of this was on one of our trips to the Kimberly where we camped on a spot that we had surfaced the year before. We ran out of time so covered our working, placed grass on top of it so absolutely no one could see any sign of detector activity, and decided to revisit the surfaced patch the following year. A continuation of the surfacing soon revealed many more small pieces and even though the gold was only small walking away from it would have left us wondering what could have been. We went from finding a few small detectable targets in close proximity to ending up with what I think was "thirty five" small pieces for only a very small amount of extra work with the pick. Some beginners will walk for kilometres down a creek to get the odd nugget only to find a more experienced operator spending the same amount of time on a hundred metre stretch of the same creek unearthing many more nuggets for a little bit of extra work with a shovel or pick.

When we work a section of creek that has produced a few nuggets we tend to leave the shallow holes unfilled for the duration of our working. This will often show us a clearer map in more detail where the drop out zones during floods occurred. Quite often you might find a larger boulder, tree root, stump, bench, close to a detected nugget, and removing some overburden can often expose some more pieces that would ordinarily have had the operator walk away from. Extra work very often is rewarded with extra success. Same goes for sections of creek that may have false or clay bottoms. Cracks in these bottoms quite often have nuggets fall into them and if the bottom is relatively shallow some "surfacing" should also be considered if a couple of nuggets have already come to light. Remember that there are many nuggets just outside the detectors reach and quite often removing only a few centimetres can make all the difference for success. I have surfaced some creeks, especially in WA, for sometimes a length of ten metres if the gravel is only shallow and been rewarded with numerous nuggets missed by hasty operators chasing only the obvious targets. Coming back later and changing up in coil size before you walk off completely, and looking for those bigger deeper targets is also recommended. Once you find gold stay a while and look outside the obvious square. Ask yourself "have I got it all". Nothing worse than a mate saying after the next flood..."you should see what you left behind buddy". :rolleyes:

DSC_8929.JPG Budgie nugget.jpg
Surfacing a bench as shown in the above photo, will more often than not expose nuggets not normally in the detectors range. Here we converted a few nuggets into almost an ounce. The "Budgie Nugget" below, was found surfacing a sloping rock bar after finding a 3-gram piece. In this instance, we converted a 3-gram piece into an additional 28-gram piece for only a little more effort. Please note, this surfacing was completely restored to original ground level as we intend to re-work this bench next winter.

One thing I cannot stress enough is when you do eventually give up on that spot you have diligently worked, "always fill in your holes" and completely "cover up" your tracks. You may want to come back at a future date with new technology and the last thing you want is the place completely stripped by other operators, especially experienced ones who can distinguish the small tell tail signs of where previous nuggets were unearthed.. Best other operators walk past hearing no targets and thinking "no gold here mate". Break a gold bearing creek into say two hundred metre sections working up and down that section several times on both banks and mid creek before starting on the next section. Don't just blindly walk down the creek for a kilometre or more, even if you think you are working efficiently....chances are you are not. On so many occasions one will find no targets working down a creek only to find they ping one on the return trip, and virtually over the same spot as previously detected. Got to do with coil orientation and many times a different approach will pick out that previously missed target. Covering distance is not the main aim when detecting. Covering every square inch is what is of the utmost importance. This doesn't happen by trying to race your mate down the creek. I'm sure many new to the game come back at the end of the day and say to their mate..."detected hundreds of square metres", down a creek, for not much results, when in fact they covered less than 10% of the available ground efficiently....see it all the time. 😢

Technique can often play a big role in finding those subtle soft targets that many often miss. This may sound controversial to some, but in "My" opinion scraping coils on the ground in this day and age, is often the difference between success and failure when already on proven ground. Skid plates are cheap. The exception to scraping is the obvious such as patch hunting. Once on the gold, having your coil on the ground and listening to those super soft targets is what will give you the advantage over the next operator, as unfortunately the size of the nuggets are getting smaller and harder to distinguish with every season. There's a lot of experienced operators using the same top of the line detectors these days so no shortage of competition for a limited number of nuggets. Some disagree on scraping as certain detectors and coils are susceptible to "coil knocking," and "falsing" often occurs when scraped. I find this is more of a problem when the detector is set too high in its sensitivity settings, running too noisy, or swinging too fast. I prefer to set a detector to run as quietly as possible with a smooth threshold and if this means slightly lowering the sensitivity then so be it. At the end of the day a quiet detector will out perform a noisy one on "nearly" all occasions for general use, and pick up subtle targets a chattery machine often misses. Low and slow is recommended for good reason if you want consistent success. Please note that this thread is targeted at the "beginners" as those with the years under their belts would find much of this as "experience already learned". Good luck out there and may the gold be kind to you....Wal.
 
Last edited:
Yes Wal, that was me. My second nugget was 35g and we packed up camp and headed for new ground. The following morning I showed off my nugget and was told "You never leave a spot like that". So we drove straight back and pulled a 6g piece out less that a metre away. The following year we spent as week or so in that spot with the new SDC2300 and was well rewarded with multiple nuggets each day.
 
Yes Wal, that was me. My second nugget was 35g and we packed up camp and headed for new ground. The following morning I showed off my nugget and was told "You never leave a spot like that". So we drove straight back and pulled a 6g piece out less that a metre away. The following year we spent as week or so in that spot with the new SDC2300 and was well rewarded with multiple nuggets each day.
Happens all the time Moneybox....I'd like a nugget for every time an operator walked away from gold. Glad to hear that you have now an altered approach, and spend more time on the gold at hand, rather than chasing the gold over the horizon.;)
 
Last edited:
Happens all the time Moneybox....Id like a nugget for every time an operator walked away from gold. Glad to hear that you have now an altered approach, and spend more time on the gold rather than chasing the gold over the horizon.;)
Was doing a search one day and found some very old scrapings & dry blowings on a slope leading down to a creek. So I stopped and put the 18" on my SD2100 and wandered down the creek. Woopee, up came a 13.5 grammer and not 10 metres further on a 12.5g was in my jar. About 50 metres further on there was a natural rock bar completely crossing the creek. Crack of dawn the next day I was back there with a shovel and spent an hour digging away the metre of sand up against the bar. Swung the detector and it went crazy by the time the sun was dipping I had over 1 1/2 ounces.
Every year since then I returned and never failed to find AU, about 5 ozs last count came out of 100 metres of that creek. I often wonder how much the Oldtimers got on the slope and if they're looking down seeing what they missed just below their workings. Have worn the 13.5g around my neck since then.Pendant.jpg
 
Wal, what an excellent, well thought out and written post, thank you for the time and effort taken by you, I'm sure it will help many including myself to become better, thanks again

Thanks Jamie,...I have a lot of time for the newcomers to our hobby and as such like to lessen the learning curve where I can and put as many as I can on the right track to enjoying this hobby. Research is something that they must do themselves, and is as important as detecting advice, but if they learn to look outside the obvious square then half the battle is already won.
 
Was doing a search one day and found some very old scrapings & dry blowings on a slope leading down to a creek. So I stopped and put the 18" on my SD2100 and wandered down the creek. Woopee, up came a 13.5 grammer and not 10 metres further on a 12.5g was in my jar. About 50 metres further on there was a natural rock bar completely crossing the creek. Crack of dawn the next day I was back there with a shovel and spent an hour digging away the metre of sand up against the bar. Swung the detector and it went crazy by the time the sun was dipping I had over 1 1/2 ounces.
Every year since then I returned and never failed to find AU, about 5 ozs last count came out of 100 metres of that creek. I often wonder how much the Oldtimers got on the slope and if they're looking down seeing what they missed just below their workings. Have worn the 13.5g around my neck since then.View attachment 5108

Beautiful nugget there Nightjar, and for those that put the extra effort in, they deserve the rewards which comes with it. I hear too often that all the good gold is already gone, but to that I say, put in the extra yards.....success will usually follow and you then start making your own luck.
 
Last edited:
Thanks Jamie,...I have a lot of time for the newcomers to our hobby and as such like to lessen the learning curve where I can and put as many as I can on the right track to enjoying this hobby. Research is something that they must do themselves, and is as important as detecting advice, but if they learn to look outside the obvious square then half the battle is already won.
Well Wal... I looked into detecting about ten years ago... and ONLY found about 10% of the direct-knowledge that you share freely in this forum... I decided 10 yrs ago that I did not have the knowledge at the time... and that was correct... as I did not have access to this forum... nor to the experience of decades of "you lot" {said in the kindest way... remember that dude from the ABC Gardening show that lives on his property at Roseveares Tasmania when he used to say "thats your bloomin lot this week"}… I am excited {in a quiet sort of way… like a maturing bottle of wine just chilling here…}… and looking forward to exiting Nth NSW and living in my car... I have always "found" things relatively easily... When on King Island the locals were astounded that I found the biggest quantity of Killakranky Diamonds that any had found in a day (small quartz bits).. just a tourist thing..ö I gave them back to them... I am sure they put them back where they came from... back in the crevices I scratched them from... "Anyhow.... "… as Hoges would say.... I am not here to prove anything but definitly here to learn the Trade of Successful Fossicking in Australia... not for monitory value... but that is useful to buy a new car as my 1999 Camry is certainly on its last legs. .. unwards and upwards... cheers... {n thanks Wal and others for your valued sharing... as my son says "Sharing is caring"… so true... ✔️✔️✔️
 
Well Wal... I looked into detecting about ten years ago... and ONLY found about 10% of the direct-knowledge that you share freely in this forum... I decided 10 yrs ago that I did not have the knowledge at the time... and that was correct... as I did not have access to this forum... nor to the experience of decades of "you lot" {said in the kindest way... remember that dude from the ABC Gardening show that lives on his property at Roseveares Tasmania when he used to say "thats your bloomin lot this week"}… I am excited {in a quiet sort of way… like a maturing bottle of wine just chilling here…}… and looking forward to exiting Nth NSW and living in my car... I have always "found" things relatively easily... When on King Island the locals were astounded that I found the biggest quantity of Killakranky Diamonds that any had found in a day (small quartz bits).. just a tourist thing..ö I gave them back to them... I am sure they put them back where they came from... back in the crevices I scratched them from... "Anyhow.... "… as Hoges would say.... I am not here to prove anything but definitly here to learn the Trade of Successful Fossicking in Australia... not for monitory value... but that is useful to buy a new car as my 1999 Camry is certainly on its last legs. .. unwards and upwards... cheers... {n thanks Wal and others for your valued sharing... as my son says "Sharing is caring"… so true... ✔️✔️✔️

Thanks Sam...interesting info about the Killiecrankie diamonds mate as they are not "small quartz bits". They are in fact Topaz that was formed some 370 million years ago, and are extremely sought after by the Lapidary community. They are referred to as diamonds as when cut into a "Brilliant cut" they very much look like diamonds with their extremely bright lustre.. I doubt that they would have put them back but instead made a good profit selling them to the tourists. ;) Good luck on the next adventure mate.
 
Once I find a bit I go over the area thoroughly.
Just take my time and slow right down.
All the bits I got yesterday were all in the same area.
Problem is they were all so tiny 😆
Size doesn't matter SL even though the misses might disagree with you, 🤔😊...covering every inch from all directions is what counts and by the pics you post you seem to do that extremely well. The big one will eventually have your name on it.
 
Thanks Sam...interesting info about the Killiecrankie diamonds mate as they are not "small quartz bits". They are in fact Topaz that was formed some 370 million years ago, and are extremely sought after by the Lapidary community. They are referred to as diamonds as when cut into a "Brilliant cut" they very much look like diamonds with their extremely bright lustre.. I doubt that they would have put them back but instead made a good profit selling them to the tourists. ;) Good luck on the next adventure mate.
I thought I would leave it to you to pick up on that (as I felt sure you would). And of course it is Flinders Island (and yes, I am having increasing problems with time remembering localities). Those whites cut up really well (I have never seen much in the way of good colours from there). I would not hand them back - might give them to friends to cut.

We used to think it a good locality when I was a geology student 55 years ago - and it seems to keep giving,
 
One thing I have noticed with some friends who tag along with us on detecting trips is that they find a piece of gold, quickly go over the area, and then walk on far too soon in an attempt to cover as much ground as they can. When detecting in creek beds gold rarely deposits in singular pieces, so if you find a piece, the chances of more being very close is extremely high. Gold is a very communal metal that likes hanging around with its mates.;) Most know the saying "Go low and go slow" but not enough beginners know that you "don't leave gold to find gold". If you find a couple of pieces in close proximity on say an inside creek bend, or bench, and hear no more obvious targets, don't just walk off thinking you have got it all. A small amount of "surfacing" by taking ten centimetres off the surface can very often expose "nests" of small nuggets just outside the reach of what you have already detected. We do this when chasing Reef gold, but not enough new to the game do this when hunting alluvial as well, instead they ping a small nugget and walk away too soon, hastily chasing the next piece.

View attachment 5104 View attachment 5105
Something as simple as removing the grass from around a detected nugget, can often dramatically increase the total number of your finds. In this instance, we converted 4 small nuggets into 28... Most would have walked away and been happy with just the four.

A very clear case of this was on one of our trips to the Kimberly where we camped on a spot that we had surfaced the year before. We ran out of time so covered our working, placed grass on top of it so absolutely no one could see any sign of detector activity, and decided to revisit the surfaced patch the following year. A continuation of the surfacing soon revealed many more small pieces and even though the gold was only small walking away from it would have left us wondering what could have been. We went from finding a few small detectable targets in close proximity to ending up with what I think was "thirty five" small pieces for only a very small amount of extra work with the pick. Some beginners will walk for kilometres down a creek to get the odd nugget only to find a more experienced operator spending the same amount of time on a hundred metre stretch of the same creek unearthing many more nuggets for a little bit of extra work with a shovel or pick.

When we work a section of creek that has produced a few nuggets we tend to leave the shallow holes unfilled for the duration of our working. This will often show us a clearer map in more detail where the drop out zones during floods occurred. Quite often you might find a larger boulder, tree root, stump, bench, close to a detected nugget, and removing some overburden can often expose some more pieces that would ordinarily have had the operator walk away from. Extra work very often is rewarded with extra success. Same goes for sections of creek that may have false or clay bottoms. Cracks in these bottoms quite often have nuggets fall into them and if the bottom is relatively shallow some "surfacing" should also be considered if a couple of nuggets have already come to light. Remember that there are many nuggets just outside the detectors reach and quite often removing only a few centimetres can make all the difference for success. I have surfaced some creeks, especially in WA, for sometimes a length of ten metres if the gravel is only shallow and been rewarded with numerous nuggets missed by hasty operators chasing only the obvious targets. Coming back later and changing up in coil size before you walk off completely, and looking for those bigger deeper targets is also recommended. Once you find gold stay a while and look outside the obvious square. Ask yourself "have I got it all". Nothing worse than a mate saying after the next flood..."you should see what you left behind buddy". :rolleyes:

View attachment 5106 View attachment 5107
Surfacing a bench as shown in the above photo, will more often than not expose nuggets not normally in the detectors range. Here we converted a few nuggets into almost an ounce. The "Budgie Nugget" below, was found surfacing a sloping rock bar after finding a 3-gram piece. In this instance, we converted a 3-gram piece into an additional 28-gram piece for only a little more effort. Please note, this surfacing was completely restored to original ground level as we intend to re-work this bench next winter.

One thing I cannot stress enough is when you do eventually give up on that spot you have diligently worked, "always fill in your holes" and completely "cover up" your tracks. You may want to come back at a future date with new technology and the last thing you want is the place completely stripped by other operators, especially experienced ones who can distinguish the small tell tail signs of where previous nuggets were unearthed.. Best other operators walk past hearing no targets and thinking "no gold here mate". Break a gold bearing creek into say two hundred metre sections working up and down that section several times on both banks and mid creek before starting on the next section. Don't just blindly walk down the creek for a kilometre or more, even if you think you are working efficiently....chances are you are not. On so many occasions one will find no targets working down a creek only to find they ping one on the return trip, and virtually over the same spot as previously detected. Got to do with coil orientation and many times a different approach will pick out that previously missed target. Covering distance is not the main aim when detecting. Covering every square inch is what is of the utmost importance. This doesn't happen by trying to race your mate down the creek. I'm sure many new to the game come back at the end of the day and say to their mate..."detected hundreds of square metres", down a creek, for not much results, when in fact they covered less than 10% of the available ground efficiently....see it all the time. 😢

Technique can often play a big role in finding those subtle soft targets that many often miss. This may sound controversial to some, but in "My" opinion scraping coils on the ground in this day and age, is often the difference between success and failure when already on proven ground. Skid plates are cheap. The exception to scraping is the obvious such as patch hunting. Once on the gold, having your coil on the ground and listening to those super soft targets is what will give you the advantage over the next operator, as unfortunately the size of the nuggets are getting smaller and harder to distinguish with every season. There's a lot of experienced operators using the same top of the line detectors these days so no shortage of competition for a limited number of nuggets. Some disagree on scraping as certain detectors and coils are susceptible to "coil knocking," and "falsing" often occurs when scraped. I find this is more of a problem when the detector is set too high in its sensitivity settings, running too noisy, or swinging too fast. I prefer to set a detector to run as quietly as possible with a smooth threshold and if this means slightly lowering the sensitivity then so be it. At the end of the day a quiet detector will out perform a noisy one on "nearly" all occasions for general use, and pick up subtle targets a chattery machine often misses. Low and slow is recommended for good reason if you want consistent success. Please note that this thread is targeted at the "beginners" as those with the years under their belts would find much of this as "experience already learned". Good luck out there and may the gold be kind to you....Wal.
Points well made - mechanical concentration processes will usually be working on more than one bit of alluvial gold. Most detecting on reefs understand the need not to walk away after the first find. Gold concentrates chemically in quartz reefs as well, so few lumps of gold in reefs are solitary too. I've seen it with a mate who pulled 20 oz out of a reef the first day, focusing just on a small area. Went back and did the same small area and its margins the next day - got another 10 ounces....
 
I thought I would leave it to you to pick up on that (as I felt sure you would). And of course it is Flinders Island (and yes, I am having increasing problems with time remembering localities). Those whites cut up really well (I have never seen much in the way of good colours from there). I would not hand them back - might give them to friends to cut.

We used to think it a good locality when I was a geology student 55 years ago - and it seems to keep giving,

I have a handful from a mate in Tassie and facetted a couple of them myself. One was a very clear white which I needed to recut as the first attempt at the table was too close to the cleavage plane and the polishing was not up to scratch. Came out OK eventually though. The second was a stone with a yellowish tint and it won a comp for me so something must have gone right with that one. You are right though goldie with the location. Most from there are not quite what I would call faceting grade material because of fractures and definitely not as good as the ones on mainland Tassie around the Weld River region. My favourite facet grade material still comes from O'briens Creek in QLD and as such we visit that location quite often from return trips to WA chasing gold.
 
Thanks Sam...interesting info about the Killiecrankie diamonds mate as they are not "small quartz bits". They are in fact Topaz that was formed some 370 million years ago, and are extremely sought after by the Lapidary community. They are referred to as diamonds as when cut into a "Brilliant cut" they very much look like diamonds with their extremely bright lustre.. I doubt that they would have put them back but instead made a good profit selling them to the tourists. ;) Good luck on the next adventure mate.
Gee... I literally had a full overflowing handful from a few hours of fossicking,... that, OBVIOUSLY, the locals would not have tossed back... ah well... life hey... ha!
 
Gee... I literally had a full overflowing handful from a few hours of fossicking,... that, OBVIOUSLY, the locals would not have tossed back... ah well... life hey... ha!
Quartz in some of its crystalline form can have a very bright lustre. On a trip many years ago we did a vid on the Nundle crystals, which are some of the clearest in Australia. Liz made reference to them as "Nundle Diamonds" and for some reason this description stuck with many within the Lapidary community, and they are now commonly referred to as "Nundle Diamonds." 😮 Similar story with the "Herkimer diamonds" which are found in the Herkimer County in the US. They are double terminated "Quartz " crystals, so although general Quartz is not of much interest, certain varieties are so special that they get a "Diamond " label.😊
 
Quartz in some of its crystalline form can have a very bright lustre. On a trip many years ago we did a vid on the Nundle crystals, which are some of the clearest in Australia. Liz made reference to them as "Nundle Diamonds" and for some reason this description stuck with many within the Lapidary community, and they are now commonly referred to as "Nundle Diamonds." 😮 Similar story with the "Herkimer diamonds" which are found in the Herkimer County in the US. They are double terminated "Quartz " crystals, so although general Quartz is not of much interest, certain varieties are so special that they get a "Diamond " label.😊
Lustre is an interesting property of a mineral, and is not a single, non-variable property of a mineral (hence your observations) - it can aid identification but is rarely as unique as something like hardness (although even Mohs hardness can vary with orientation in some minerals). To some degree it is a mineral's "sparkle". Scientifically, it is related to the capacity of a mineral surface to reflect visible light, the intensity of that reflected light (and therefore os a minerals' lustre depending on "the refractive index, absorption coefficient and reflectivity of the mineral".#

https://geology.com/minerals/luster.shtml#diagnostic
This is one of the best descriptions I have found that discusses it in relation to gems "Gemologists put more work into their assessment of luster. They also use luster in gem identification in more ways than geologists use it in mineral identification. A gemologist might report:

dot2.gif
a general luster for a mineral (gem) species
dot2.gif
a general luster for a mineral (gem) variety
dot2.gif
a fracture surface luster
dot2.gif
a cleavage surface luster
dot2.gif
a polished surface luster
In corundum (including ruby and sapphire corundum), basal parting planes can exhibit a pearly or submetallic luster. This differs from the vitreous to adamantine luster that might be observed on crystal and fracture faces. A pearly luster on parting planes can indicate that the material might display asterism if cut properly. Gemologists pay attention to luster because, after color, luster is the most obvious property of an item that will be sold for tens, hundreds, thousands, or millions of dollars". Hardness is also important (and why we have doublets for opal etc. - some gems are soft enough to scratch or porous enough to absorb liquids and discolour.

(#The refractive index of a gemstone measures the difference between the speed of light in air and the speed of light in the gemstone. This is determined by the gemstone’s angle of refraction. Every gemstone has a unique refractive index, meaning every gemstone refracts light at a unique angle. The higher the refractive index, the greater the amount of dispersion, which increase the brilliance of a material. Strictly, for many minerals refractive index varies with the direction that light travels through a mineral (so some minerals can look black under a microscope if you are looking down a particular mineral axis, e.g. the c axis of quartz).

The absorption coefficient determines how far into a material light of a particular wavelength can penetrate before it is absorbed. For example, some minerals are transparent in thin slivers but opaque when thicker, e,g, cinnabar.

The reflective index is the percentage of light that bounces off the solid surface and is not absorbed)

Rather technical, I know, but might interest those who cut their own gems - I sort of knew it, but had not really put the various properties together until I saw this, and it explains the variation you have seen. It is no wonder it is important to gemologists.
 
Very comprehensive goldie and of much interest to the lapidary members here on the Forum...all Quartz is not boring even though some of the gold bearing quartz might not float your boat...unless of course it is riddled with gold 😊...then it has my total undivided attention.
 
Last edited:
Lustre is an interesting property of a mineral, and is not a single, non-variable property of a mineral (hence your observations) - it can aid identification but is rarely as unique as something like hardness (although even Mohs hardness can vary with orientation in some minerals). To some degree it is a mineral's "sparkle". Scientifically, it is related to the capacity of a mineral surface to reflect visible light, the intensity of that reflected light (and therefore os a minerals' lustre depending on "the refractive index, absorption coefficient and reflectivity of the mineral".#

https://geology.com/minerals/luster.shtml#diagnostic
This is one of the best descriptions I have found that discusses it in relation to gems "Gemologists put more work into their assessment of luster. They also use luster in gem identification in more ways than geologists use it in mineral identification. A gemologist might report:

dot2.gif
a general luster for a mineral (gem) species
dot2.gif
a general luster for a mineral (gem) variety
dot2.gif
a fracture surface luster
dot2.gif
a cleavage surface luster
dot2.gif
a polished surface luster
In corundum (including ruby and sapphire corundum), basal parting planes can exhibit a pearly or submetallic luster. This differs from the vitreous to adamantine luster that might be observed on crystal and fracture faces. A pearly luster on parting planes can indicate that the material might display asterism if cut properly. Gemologists pay attention to luster because, after color, luster is the most obvious property of an item that will be sold for tens, hundreds, thousands, or millions of dollars". Hardness is also important (and why we have doublets for opal etc. - some gems are soft enough to scratch or porous enough to absorb liquids and discolour.

(#The refractive index of a gemstone measures the difference between the speed of light in air and the speed of light in the gemstone. This is determined by the gemstone’s angle of refraction. Every gemstone has a unique refractive index, meaning every gemstone refracts light at a unique angle. The higher the refractive index, the greater the amount of dispersion, which increase the brilliance of a material. Strictly, for many minerals refractive index varies with the direction that light travels through a mineral (so some minerals can look black under a microscope if you are looking down a particular mineral axis, e.g. the c axis of quartz).

The absorption coefficient determines how far into a material light of a particular wavelength can penetrate before it is absorbed. For example, some minerals are transparent in thin slivers but opaque when thicker, e,g, cinnabar.

The reflective index is the percentage of light that bounces off the solid surface and is not absorbed)

Rather technical, I know, but might interest those who cut their own gems - I sort of knew it, but had not really put the various properties together until I saw this, and it explains the variation you have seen. It is no wonder it is important to gemologists.
FYI... The RI... refractive index, applies exactly the same to traditional archival quality, oil painting.... ... . A whole study of HOW the artist, Rubens (for example) achieved such a brilliant-lustre from his paintings, (when others, did not, or could not do so)… is found in the study of the RI knowledge and HOW to do so... and crushed lead crystal-quartz is part of that open secret... as well as multiple layers of transparent paints, thus the light can get in, as well as refract out of the surface layers of the paintings... thus the effect of brilliance is found upon the eye...
 
Excellent post and a great reminder. I know when I've found gold in a virgin spot, I immediately think "patch" and scoot off in every direction trying to find the next piece. When that fails I take a breath, walk back to where the nugget was, and carefully detect the immediate area round the hole, and then start spiralling or gridding out, whatever is more appropriate for the terrain. They are very rarely a loner
 

Latest posts

Top