❓Your Mineral Identification Questions answered here

[Lefty]

Sorry Lefty, I missed your reply.

That stone was found close to a basalt headland near Kiama and there are literally thousands of similar stones just in the one spot. Definitely a volcanic area but I have never seen any specific mention of rhyolite.

No worries mate.

As Goldirocks has previously mentioned, it's quite common for one area of volcanic geology to be heavily dominated by one particular type of volcanics while still containing a smattering of little patches of different types.

I've been in a number of areas marked as felsic volcanics (high-silica lavas including rhyolite) on the geo map and come across tiny little areas that appear a completely different kind ie, mafic (high iron and magnesium) lavas.

Basalt is mafic - I guess the reverse might be possible and there may be little patches of felsic stuff in the same area dominated by mafics?

 

[user 4386]

Sorry Lefty, I missed your reply.

That stone was found close to a basalt headland near Kiama and there are literally thousands of similar stones just in the one spot. Definitely a volcanic area but I have never seen any specific mention of rhyolite.

No worries mate.

As Goldirocks has previously mentioned, it's quite common for one area of volcanic geology to be heavily dominated by one particular type of volcanics while still containing a smattering of little patches of different types.

I've been in a number of areas marked as felsic volcanics (high-silica lavas including rhyolite) on the geo map and come across tiny little areas that appear a completely different kind ie, mafic (high iron and magnesium) lavas.

Basalt is mafic - I guess the reverse might be possible and there may be little patches of felsic stuff in the same area dominated by mafics?

Yes, the reverse also occurs. It depends a bit on where you are. For example you will not find both together very often on the basalt lava plains of Victoria, although you do find little clusters (eg trachytes around Mount Macedon area, a bit around Omeo). It is far more common to find both together in some areas of eastern and central-western NSW and eastern Queensland, and a classic would be the area around Pambula NSW (the Boyd Volcanics). Often called bimodal volcanics (two modes - basalt and say rhyolite, thought to occur at the bottom and top of single magma chambers, respectively). So most of the time you get basalt flows but then a bit of rhyolite will be tapped and come to surface. Important in a lot of epithermal gold areas such as Nevada, Phillipines, Indonesia and Pacific Islands. I would suspect the area around Coonabarabran and the Glasshouse Mountains might also be of this type. Also important for some gems as we have discussed. The "greenstone belts" of the Eastern goldfields, WA are similar ancient examples - most of the volcanics are metamorphosed basalts etc (greenstone - metamorphism converts them to green minerals like chlorite and amphiboles) but there are minor rhyolites and porphyry intrusions within them.

 

[Danbob]

I'll buy slag. I would have thought that the first two would be harder than your streak plate - so that the streak plate would powder not the sample. And do you mean white? The first may be rhyolite, then jasper. And the concretion may be limonite around a tree root. Not sure you need much help.....

Aplolgies goldierocks, my response was a little rushed. Those two stones easily scratched the plate and left behind a white powder (not colourless), which belonged to the porcelain only. As for not needing much help - it is the information that I have been reading on this forum for the last eighteen months (provided by people such as yourself) that has enabled me to at least form a cursory opinion about the various minerals I collect. Many thanks!

In fact, you are both spot on the money regarding my first two stones - it just took someone to put it in plain English to a relative newbie such as myself. The area in question is definitely mafic but with several small pockets of stones which appear to have no place being there, being of a much higher quartz content than the surrounding rocks. Incidentally, I have several other rough stones trimmed down ready to cab and I am amazed at some of the colours I have found amongst these.

Thanks also for leading me in the right direction with the other pieces - shame about the slag!

Cheers...

 

[Mackka]

Illawarra, dead give away for slag. Port Kembla Steel Works at Cringila, I remember as a boy seeing these plumes of yellow, red clouds spewing forth into the atmosphere and thinking , wow, how beautiful is that. Now I know better and so do they.
Had a friends brother did at Mt. Kembla on a trail bike.
Cheers
Mackka

 

[Danbob]

G'day Mackka,

Yes, the slag is an 'occupational' hazard for any budding rock hound in our area and I hate to say it but it's not the first time I've been caught! At least this lump looks pretty.

Cheers...

 

[Mackka]

Hahaha, you should have heard the "explosion sounds" as the slag hit the water next to the rail line . Ka boom . Just magnificent for a very young impressive boy.
Mackka

 

[user 4386]

I'll buy slag. I would have thought that the first two would be harder than your streak plate - so that the streak plate would powder not the sample. And do you mean white? The first may be rhyolite, then jasper. And the concretion may be limonite around a tree root. Not sure you need much help.....

Aplolgies goldierocks, my response was a little rushed. Those two stones easily scratched the plate and left behind a white powder (not colourless), which belonged to the porcelain only. As for not needing much help - it is the information that I have been reading on this forum for the last eighteen months (provided by people such as yourself) that has enabled me to at least form a cursory opinion about the various minerals I collect. Many thanks!

In fact, you are both spot on the money regarding my first two stones - it just took someone to put it in plain English to a relative newbie such as myself. The area in question is definitely mafic but with several small pockets of stones which appear to have no place being there, being of a much higher quartz content than the surrounding rocks. Incidentally, I have several other rough stones trimmed down ready to cab and I am amazed at some of the colours I have found amongst these.

Thanks also for leading me in the right direction with the other pieces - shame about the slag!

Cheers...

You are welcome - but clearly on the right track

 

[Danbob]

Hahaha, you should have heard the "explosion sounds" as the slag hit the water next to the rail line . Ka boom . Just magnificent for a very young impressive boy.
Mackka

Funny you should mention that! I worked in the steelworks for a decade and definitely had some first-hand experience with those loud bangs - sometimes a little too close for comfort...... 8)

Cheers...

(Edit - grammar)

 

[Chiron52]

I too worked at the steelworks for about 20yrs.
As kids we lived at Mt.Kembla and every spare minute we could get was spent exploring the mountain range. We found the remains of old miners huts, fruit orchards in the middle of thick bush and even a few descendants of the old pit ponies that had been used to haul coal out of the mines in the old days.
We spent a lot of time around the Mt Kembla, Nebo and Kemira collieries searching through the waste dumps to see what the miners had chucked out (found an old violin, a tin of 45? caliber bullets, etc. Also found many fossils in the waste rocks.)
The base used for the rail tracks from Port Kembla up to the pits, was all slag from the steelworks. I remember it being of various colours too.

Note: Mount Kembla Mine Disaster.
The Mount Kembla Mine disaster was the worst post-settlement peace-time disaster of Australia's history, until the 2009 Black Saturday bushfires in Victoria. It occurred at the colliery adjacent to the village at 2pm on 31 July 1902. The explosion was caused by ignition of gas and coal dust by flames used as torches by the miners. 96 workers - men and boys, were killed by the explosion. Hundreds of people helped in the rescue of survivors.

A quote from the mine manager, William Rogers, stated that the mine was "absolutely without danger from gases", the Illawarra Mercury reported that "gas had never been known to exist in the mine before" and The Sydney Morning Herald recorded "one of the best ventilated mines in the State".[5]

However, after the explosion left 33 widows and 120 fatherless children; an inquiry returned a conclusion that Mount Kembla Mine was both gassy and dusty and that the Meurant brothers and William Nelson "came to their death from carbon monoxide poisoning produced by an explosion of fire-damp ignited by the naked lights in use in the mine, and accelerated by a series of coal-dust explosions starting at a point in or about the number one main level back headings, and extending in a westerly direction to the small goaf, marked 11 perches on the mine plan."

 

[Wally69]

Any ideas what this ??? It turned up in a bag of goodies I acquired.

 

[Wally69]

And this one

 

[Gilly47]

I personally have NO idea. But it is a very nice one

ray

 

[Chlomax]

Hi everyone,
A little newbie fossicker over here. I come across this little stone after my old panning remains dried. Located just north of Dargo. Its only small but the colour of pink caught my eye. The others I found were more of an orange pink. Any insight anyone could provide would be amazing! Thank you

 

[user 4386]

Bigger photo would help! Garnet perhaps.

 

[Heatho]

It looks like a pink sapphire or rhodolite garnet to me, as Goldierocks said a larger photo would really help. Pink sapphires/rubies will generally flouresce under a UV light if you have one.

Welcome to the forum.

 

[user 4386]

Rubies are scarcer than hen's teeth in Victoria - in fact I am not sure if more than the single crystal near Gembrook has ever been substantiated. Lots of claimed rubies but they don't stand up when investigated by mineralogists (eg Bill Birch at Museum Victoria). So more likely pyrope garnet (called rhodolite when gem quality) - common throughout much of Victoria, mostly in areas of granodiorite ("granite") and felsic volcanics of Devonian age. Dargo is one such area.

 

[Lefty]

So more likely pyrope garnet (called rhodolite when gem quality) - common throughout much of Victoria, mostly in areas of granodiorite ("granite")

Interesting.

The area where I get my amethyst is marked on the geo map as a fair sized patch of granodiorite. Can't find the reference now but was shown a very old (pre-1900) gold mining report in the area that reported finding "small rubies".

Anything is possible I guess but far more likely to be garnets I imagine. Now I would love to find rubies but as a fossicker and a gem cutter, I'd still be happy finding some nice rhodolite garnet that wasn't too dark.

 

[snafu]

There's a spot south of Bingara that was named Ruby Hill back in the early days, but what was thought to be rubies turned out to be pyrope garnet. I had a scratch there a few years ago and managed to pick up about a matchbox full in a couple of hours. Nice colour, but very tiny stones.

I've often wondered how Ruby Hill here in Sapphire got it's name. I know a lot of blokes who are mining there, some of them for close on 40 years, but not one has ever reported a ruby find or maybe they just don't want to say much.

Jeff

 

[LONEWOLF]

The old timers were caught out at Ruby Hill in the Harts Range NT too.... Anything Red in those days was called Ruby...

LW....

 

[Lefty]

There's a spot south of Bingara that was named Ruby Hill back in the early days, but what was thought to be rubies turned out to be pyrope garnet. I had a scratch there a few years ago and managed to pick up about a matchbox full in a couple of hours. Nice colour, but very tiny stones.

I've often wondered how Ruby Hill here in Sapphire got it's name. I know a lot of blokes who are mining there, some of them for close on 40 years, but not one has ever reported a ruby find or maybe they just don't want to say much.

Jeff

I read a report written in the very earliest days of the field in the late 1800's, a geologist described a parti sapphire that had a patch of definate red in it that would technically be a ruby if the rest of the stone were cut away. But my mate had a machinery lease out there for years and in all that time he found three small pink sapphires.

You ever found any garnets there Jeff? We never have , same mate said he found one about the size of a grape - the only one he ever found there.