❓Your Mineral Identification Questions answered here

[user 4386]

In summary, horses for courses. If you want red stones and chromium makes them red they need to form in a chromium rich rock (so Burma has these and has lots of red rubies and coloured spinel). But if the rock they form in is iron-rich (as in eastern Australia), you will get blue sapphires (which like rubies are the same mineral corundum, just blue not red), and will mostly get unattractive and dark iron-rich spinels, not coloured ones.

Some of the guys here know lots about mineralogy and chemistry, others are newcomers, but I can pitch at whatever level is wanted. It is a rather specialist field after all.

I checked and coloured spinel appears almost absent from NSW as well as Victoria and Tasmania .

What does it mean? In eastern Australia it is more productive to look for the best sapphires you can find (we used to produce 70% of the world's best blue sapphires only a few decades ago). And not spend too much time looking for rubies or gem spinel.

 

[Lefty]

Interesting stuff, thanks Goldirocks.

Does that make Burmese spinel and Ruby metamorphic in origin, coming from.......marble I guess it would be? Limestone baked by volcanics.

Ordinary black spinel actually facets quite a nice looking stone if done properly. Your standard brilliant cuts don't do much for it imo (they are really designed for transparent stones) but a checkerboard crown works nicely. It takes on an excellent polish and it hard enough to resist general wear and tear.

Interestingly, it is the only opaque black material I have ever faceted/cabbed that actually produces black swarf when ground instead of white.

 

[user 4386]

It is difficult to find good descriptions. However generalized geological descriptions that I possess mention marble, and skarn (a rock formed by reaction of fluids evolved from things like granite when it intrudes the marble). Also ultramafic rocks, which are always high in chromium.

Yes, all sorts of things can be made to look good in the right hands, but I don't much like black opaque stones myself - personal preference,. No flashes of colour and refraction, no banding or colour variation. However things like jet were quite popular in the 19th century (also black powder when ground). Yes, black spinel will take any amount of wear and tear - quite hard (one less than corundum in Moh's scale). Another fairly common stone (in appropriate mineral fields) is black diamond, which can look good as a cluster rim of tiny black around a large white diamond. Anything can look good with the right imagination and skill.

I didn't mention, but even some of the coloured spinels are slightly magnetic.

Also it depends on marketing - making people think something looks good so they will buy it. Champagne diamonds as from the Kimberleys used to be a colour so far down the list for diamonds that no one wanted them - until a good marketing exercise was put in place. White was always preferred over all else. However I was once taken in to the strongroom in the Premier mine in Pretoria (SA), surrounded by armed guards, and among the beautiful stones I saw were huge diamonds of every colour under the sun. At the time they said buyers did not much want them, but imagine vivid blues, reds and yellows in large transparent stones with the refractive index of diamond! I also saw the ore coming over the grease plates and diamonds clustering there like gravel - an amazing sight.

 

[Goldinpinecreek]

What test kit is recommended to test gold .

 

[user 4386]

What test kit is recommended to test gold .

It is yellow, it is soft and scratches with a $2 coin (or smears when rubbed on the coin), Do a tiny scratch with a mini pocket knife or needle point while looking under a hand lens - when it scratches it all stays yellow (pyrite and chalcopyrite are brittle and harder than a coin, their powder is black or greenish-black), It is malleable (if you tap it with a hammer it flattens, whereas pyrite and chalcopyrite break into a dark powder). Once seen a few times you will know it by sight as usually quite yellow,

 

[Heatho]

My preference for the ultimate black gemstone is black spinel as well, beautiful stuff when cut properly with the durability of sapphire. Anyway I was a heavy metal guitarist in another life, I like black and there is nothing blacker than a nice spinel.

 

[Lefty]

Heh, I was a headbanger in another life as well - black clothes including the obligatory Iron Maiden/Metallica/Megadeth/Slayer/Sepultura/Panterra tshirt, hair halfway down my back, car stereo thumping out albums of fore mentioned bands at about half a million decibels - those were the days

But it's surprising how many people like black stones, or sapphires so dark midnight blue or garnets so dark blood red that they appear black barring a few flashes of colour.

 

[Dihusky]

But it's surprising how many people like black stones, or sapphires so dark midnight blue or garnets so dark blood red that they appear black barring a few flashes of colour.

I think it's an overlooked marketplace, my daughter also loves black stones and has placed an order with me, just got to find something nice and refine my skills. Then we are going to take the diamonds out of a piece she was given by my now passed mother and make something new.

As she puts it, Black goes with everything, dress it up or down, it always works... and she knows how to dress!!

 

[user 4386]

Like I said - it is the marketing that makes it (one reason certain stones go in and out of fashion) - like the champagne diamonds of Argyle that you would not have been able to give away 40 or more years ago. A lot of it involves appealing to associations, and you guys have given such an example for black stones. Perhaps Jet will come back in as well (a lot softer though, so spinel makes sense).

 

[Lefty]

But it's surprising how many people like black stones, or sapphires so dark midnight blue or garnets so dark blood red that they appear black barring a few flashes of colour.

I think it's an overlooked marketplace, my daughter also loves black stones and has placed an order with me, just got to find something nice and refine my skills. Then we are going to take the diamonds out of a piece she was given by my now passed mother and make something new.

As she puts it, Black goes with everything, dress it up or down, it always works... and she knows how to dress!!

Excellent point - black goes with everything! Can't go wrong with a black stone, assuming you like them.

A dull black stone would not be very interesting I think but those such as black spinel or very dark sapphires and garnets that polish up to a brilliant, almost adamantine finish have an allure to them. A good design will cause them to throw continual brilliant flashes off the surface.

 

[Lefty]

Like I said - it is the marketing that makes it (one reason certain stones go in and out of fashion) - like the champagne diamonds of Argyle that you would not have been able to give away 40 or more years ago. A lot of it involves appealing to associations, and you guys have given such an example for black stones. Perhaps Jet will come back in as well (a lot softer though, so spinel makes sense).

The moral of the story is: never throw anything away, it might be valuable in the future!

Just like those champagne diamonds, sapphires have a similar history. When the Anakie field was first opened up in the late 1800's, a sapphire was blue. If it was not blue it was worth little or nothing. All those beautiful green, yellow and parti stones either thrown away or just stuffed in an old tobacco tin and forgotten, along with the zircons that had similar value issues, despite their fire and brilliance.

The Black Star of Queensland was considered worthless when first discovered and was supposedly used by the family as a doorstop for over a decade before being sold for a relatively modest sum. It last changed hands for $88 million US (though that figure is probably boosted by the diamonds in the setting).

 

[Heatho]

Champagne diamonds are a fantastic looking stone, white diamonds, ummm yeah, pretty boring in my opinion, I like white diamonds but everyone has one..... Gimmee nice coloured gemstones any day over white diamond.

I don't think it just comes down to marketing, people will buy what they see and like if it is available.

 

[user 4386]

It is the valuers you have to convince - in Africa it is a rigid formal process to value, and champagne was far down the list at first. A lot of people use diamonds to store wealth like they do gold. and the valuations matter. Me, I like what I like....

 

[deadpan]

In summary, horses for courses. If you want red stones and chromium makes them red they need to form in a chromium rich rock (so Burma has these and has lots of red rubies and coloured spinel). But if the rock they form in is iron-rich (as in eastern Australia), you will get blue sapphires (which like rubies are the same mineral corundum, just blue not red), and will mostly get unattractive and dark iron-rich spinels, not coloured ones.

Some of the guys here know lots about mineralogy and chemistry, others are newcomers, but I can pitch at whatever level is wanted. It is a rather specialist field after all.

I checked and coloured spinel appears almost absent from NSW as well as Victoria and Tasmania .

What does it mean? In eastern Australia it is more productive to look for the best sapphires you can find (we used to produce 70% of the world's best blue sapphires only a few decades ago). And not spend too much time looking for rubies or gem spinel.

That's totally clear to me and now makes your first post on the spinel colourings pretty much understanable also. Appreciate your your help, thank you.

 

[Heatho]

It is the valuers you have to convince - in Africa it is a rigid formal process to value, and champagne was far down the list at first. A lot of people use diamonds to store wealth like they do gold. and the valuations matter. Me, I like what I like....

Diamonds really are way overvalued to start with in my opinion and nowhere near as rare as the diamond cartels would lead us to believe.

 

[Lefty]

It is the valuers you have to convince - in Africa it is a rigid formal process to value, and champagne was far down the list at first. A lot of people use diamonds to store wealth like they do gold. and the valuations matter. Me, I like what I like....

Diamonds really are way overvalued to start with in my opinion and nowhere near as rare as the diamond cartels would lead us to believe.

My understanding was that sapphires are actually rarer overall in the geological sense but diamond mining and marketing is dominated by a global cartel which gives them a lot of pricing power.

Still, if I ever found a diamond there's no way I'd chuck it back into the creek

 

[user 4386]

I doubt that sapphires are rarer - we see them all the time in central Victoria but too small to cut in the main. I've never panned a diamond anywhere. However they are not all that rare in pipes, and De Beers would buy up competitors and close the mines, to control the flow onto the market. The best gem diamonds were on beaches in Namibia though - they had been carried hundreds of km down the Orange River to the sea and flawed diamonds broke up in the process, leaving mostly gems (gems are outnumbered by industrial diamonds in the pipes, although the giant gems are mostly from pipes).

 

[Heatho]

I'm pretty sure I found one at Oberon one time but for life of me I can't find it. It wasn't gem quality but pretty sure it was diamond as it was hydrophobic. Maybe I'm just dreaming it was but it was totally different to anything else I've ever found there.

I got a pic of it but when I went to look for it again to do an SG test I couldn't find it.

 

[user 4386]

Don't wish to be a wet blanket, but they look a bit like flakes of white mica in it, something I haven't seen in a diamond. Also, diamonds are very hard and they tend not to become rounded like that but retain cleavage faces and crystal faces. These ones have had more than 1000 km of transport down a river, then been washed around on a sea floor:

 

[Heatho]

No, was certainly not mica, was a very hard stone and bounced when dropped on concrete. Anyway I guess we'll never know what it was unless I find it again. Not something I'm losing sleep over though. :Y: