❓Your Mineral Identification Questions answered here

[user 4386]

Are there any particular locales that they are located?

Thanks!

Debbie

I think a number of fields. Most fields in Queensland (but they are dominantly boulder opal fields although vainlets occur in the same fields). Andamooka comes to mind in South Australia. It often invades the spaces between the sand grains and atb Andamooka is sold as "matrix opal" for aquariums etc (yours is an actual vein of course, but veins also occur there in sandstone). Since it is not really being sold as a gemstone for aquariums. they usually soak it in sugar solution, then acid that turns the sugar to black carbon enhancing the colour. This is what tends to occur naturally in black opal, where the black is actually a black material between the spheres that make up opal.

I don't think colours are diagnostic of any opal field. Precious opal does not have any colour in it of course. It consists of packed spheres of varying diameter that break up light passing through the opal in the way a prism or rainbow does. Patches with different diameter spheres refract light by different amounts giving different colours - there is no actual colour in precious opal. Makes it rather magical!

Opal looks like this under an electron microscope.

 

[Debbie K]

Thank you for your detailed response! I do have one piece of rough Andamooka, and the matrix of coarse sandstone does look very similar to this piece. There are some photos on mindat that look very similar, so it's very likely that this may be the source.

I think I may give it a go regarding carving the sandstone away. There is a smaller vein on the back that can try to carve to, and I'll see how that goes before I tackle the front. The front side has an area appears to be about 11 cm by 4 cm in a triangular shape, if the vein is where I think it is. The vein on the top edge is nearly 5 mm thick and then seems to get very thin towards the bottom. The problematic part of this carving is, if that is the case, it's really too big for a gemstone and probably more suitable as a display piece. If it's going to be a display piece, it might be better to leave it as a specimen. I just don't know.

Thanks again!

Re: color, I agree for the most part about it not being diagnostic of any particular location, especially for opal. The only exception I can think of is the Mexican "fire opal". That bright orange to cherry red color is pretty distinctive.

Debbie

 

[user 4386]

Thank you for your detailed response! I do have one piece of rough Andamooka, and the matrix of coarse sandstone does look very similar to this piece. There are some photos on mindat that look very similar, so it's very likely that this may be the source.

I think I may give it a go regarding carving the sandstone away. There is a smaller vein on the back that can try to carve to, and I'll see how that goes before I tackle the front. The front side has an area appears to be about 11 cm by 4 cm in a triangular shape, if the vein is where I think it is. The vein on the top edge is nearly 5 mm thick and then seems to get very thin towards the bottom. The problematic part of this carving is, if that is the case, it's really too big for a gemstone and probably more suitable as a display piece. If it's going to be a display piece, it might be better to leave it as a specimen. I just don't know.

Thanks again!

Re: color, I agree for the most part about it not being diagnostic of any particular location, especially for opal. The only exception I can think of is the Mexican "fire opal". That bright orange to cherry red color is pretty distinctive.

Debbie

Yes, but Mexican fire opal is a constant colour not a play of colours like you illustrated - really a form of common opal not precious opal. I have never been much impressed by them. Unlike our precious opal, fire opal is actually coloured - the colour being very fine inclusions of iron oxide grains.

"Mexican Fire Opals are just orange common opals that are found in Mexico and a few other locations. Their coloration ranges through the normal shades of a fire, hence the name, and they’re noted for often lacking the color play on the interior that has made opals from Australia and Ethiopia so famous".

I know a few other localities where there is a proper play of fire, notably in Brazil - also a locality in central America, but they are in a completely transparent and clear matrix, not white or black, and not as impressive.

 

[Debbie K]

Respectfully, that is not the case. I have some that does have play of color; the good stuff does. I will try to get a photo of some of it; it's rough and small and I'll probably have to mess around with lighting to get it to show. The vast majority of it is "meh", but some of it is really nice. It might be tomorrow before I get it done.

 

[user 4386]

Respectfully, that is not the case. I have some that does have play of color; the good stuff does. I will try to get a photo of some of it; it's rough and small and I'll probably have to mess around with lighting to get it to show. The vast majority of it is "meh", but some of it is really nice. It might be tomorrow before I get it done.

Yes, I have seen some - but as noted, with a transparent (and usually at least lightly coloured matrix), not white or black, sometimes with crystal inclusions. I prefer the solid matrix white or black - and yes, I occasionally see really nice fire opals, and those ones also have refracting colour properties often superimposed on a base colour..





However I find most is rather blah, more like this



And not up to a good Aussie stone

 

[MegsyB007]

Didn't I see some Aussies finding orange fire opal on 'Aussie Opal Hunters' in WA?

There are a lot of stones called 'opal' that do not match my idea of an opal.
Maybe I'm just spoiled from my grandfather showing me spectacular opals he'd mined, cut and polished, throughout my life.
I see boring orange fire opal and scoff!

And then there's the pink and blue opal found in Peru, that doesn't look like opal at all to me!

Here's a list of all the types of opals (or what they call opals) that is quite informative, if you're interested.
Although I must say the boring blue example of black opal is not the best specimen to show the play of colour of spectacular Lightning Ridge black opal.

https://geology.com/gemstones/opal/
Cheers,
Megsy

 

[user 4386]

Didn't I see some Aussies finding orange fire opal on 'Aussie Opal Hunters' in WA?

There are a lot of stones called 'opal' that do not match my idea of an opal.
Maybe I'm just spoiled from my grandfather showing me spectacular opals he'd mined, cut and polished, throughout my life.
I see boring orange fire opal and scoff!

And then there's the pink and blue opal found in Peru, that doesn't look like opal at all to me!

Here's a list of all the types of opals (or what they call opals) that is quite informative, if you're interested.
Although I must say the boring blue example of black opal is not the best specimen to show the play of colour of spectacular Lightning Ridge black opal.

https://geology.com/gemstones/opal/
Cheers,
Megsy

You say "There are a lot of stones called 'opal' that do not match my idea of an opal" The term opal is a mineralogical term for a mineral that consists of tightly-packed silica spheres - it is not quartz and is usually not coloured at all. Gemstone collectors, dealers and miners add a prefix to turn it into a name for gemstones and semi-precious stones. i.e. precious opal, black opal, common opal, wood opal.

If you have any boring blue examples of black opal like I illustrated, just send them to me (beggars can't be choosers) and I will find a use for them (mainly for my retirement fund).

 

[MegsyB007]

You say "There are a lot of stones called 'opal' that do not match my idea of an opal" The term opal is a mineralogical term for a mineral that consists of tightly-packed silica spheres - it is not quartz and is usually not coloured at all. Gemstone collectors, dealers and miners add a prefix to turn it into a name for gemstones and semi-precious stones. i.e. precious opal, black opal, common opal, wood opal.

If you have any boring blue examples of black opal like I illustrated, just send them to me (beggars can't be choosers) and I will find a use for them (mainly for my retirement fund).

LOL. I wouldn't knock it back either. It is a lovely opal, don't get me wrong. I just meant the display of colour was not great in that one. ie. Where's the most desirable/valuable red play of colour in it? Something like this is what I meant...



Now that's a sensational display of colour in a black opal!

Cheers,
Megsy

 

[user 4386]

LOL. I wouldn't knock it back either. It is a lovely opal, don't get me wrong. I just meant the display of colour was not great in that one. ie. Where's the most desirable/valuable red play of colour in it? Something like this is what I meant...

View attachment 4615

Now that's a sensational display of colour in a black opal!

Cheers,
Megsy

Agree completely

 

[Martyz]

Are there any particular locales that they are located?

Thanks!

Debbie

Hi Debbie,
Great carving you’ve done there. It’s looks like the material polished well and held together which is a good sign.
A couple of things to look for if it’s Ethiopian are:
Was it comparatively inexpensive? (Because it looks like a fair chunk)
Does slowly go clear and loose colour when Wet?
Was it difficult to get a good polish and did it stay a bit grainy after polish?
Has it cracked at all after polishing and allowing to dry completely?
These can be indicators of hydrophane opal from Ethiopia.
I’m no expert on Ethiopian opal but these seem like common issues with a lot, but not all of their opal.

 

[user 4386]

Hi Debbie,
Great carving you’ve done there. It’s looks like the material polished well and held together which is a good sign.
A couple of things to look for if it’s Ethiopian are:
Was it comparatively inexpensive? (Because it looks like a fair chunk)
Does slowly go clear and loose colour when Wet?
Was it difficult to get a good polish and did it stay a bit grainy after polish?
Has it cracked at all after polishing and allowing to dry completely?
These can be indicators of hydrophane opal from Ethiopia.
I’m no expert on Ethiopian opal but these seem like common issues with a lot, but not all of their opal.

Similar features can be a problem at Andamooka. Miners at the Stuart Ck field immediately to its north said that losses from cracking as the opal dried were very large (some even said you could hear the sound of it cracking as it dried as they drove home).

 

[Martyz]

Similar features can be a problem at Andamooka. Miners at the Stuart Ck field immediately to its north said that losses from cracking as the opal dried were very large (some even said you could hear the sound of it cracking as it dried as they drove home).

I have heard that some Australian opal with high water content can behave similarly Goldierocks.
As this was a recent purchase (online??) and there is doubt about its origin I might be thinking Ethiopian. Especially for a piece of that size if it seemed like particularly good value for money.
After looking back though Debbie’s post I realise that the doves wing wasn’t the finished piece so we’ll have to see how the material behaves when cut and polished.

 

[cha55a]

Hi all,

During a little road trip to Toodyay on the weekend, my daughter and her grandfather found a little gem/crystal store, and she persuaded him to buy her a pretty rock.

Both my daughter and father in law forgot what this is called.

Any ideas what this is?

 

[RM Outback]

Can't help you other than suggest you call or email a picture to the shop they purchased it from. Most likely someone here will be able to help. What ever it is it's a nice piece

 

[user 4386]

Can't help you other than suggest you call or email a picture to the shop they purchased it from. Most likely someone here will be able to help. What ever it is it's a nice piece

Very nice. My first guess would have been rhodochrosite (although I have never seen quite that shade). Just email the store with your image and ask. Quartz can be that colour. Hardness would probably be diagnostic, but I can understand you not wanting to damage it.

 

[MegsyB007]

Pink Cobalto Calcite maybe?

 

[user 4386]

Pink Cobalto Calcite maybe?

Of course! I think you have got it.

 

[user 4386]

Colour is spot-on!

https://llorensminerals.com/en/product/cobaltocalcite-0078/

 

[19.3]

Probably a simple ID!?
This rock came from the Turon. It sets the detector off quite strongly and is reasonably magnetic. Similar rocks nearby do not affect the detector even slightly. Magnetite? Hiw can it be magnetic but similar rocks are (probably) not?

 

[grubstake]

Probably a simple ID!?
This rock came from the Turon. It sets the detector off quite strongly and is reasonably magnetic. Similar rocks nearby do not affect the detector even slightly. Magnetite? Hiw can it be magnetic but similar rocks are (probably) not?

How big is it, mate?