What is a Black Crystal Opal?

[PinkDiamond]

Here's Paul Sedawie explaining the difference between a black opal, and a black crystal opal.

What is a Black Crystal Opal?

[SwordfishMining]

So crystal opals should be more valuable than a regular black opal with the same face up POC because they are pure opal you can see through and the eye clean ones should be super gem compared to included. If you had to choose one stone over the other at the same price point, you cant see thru the potch or non gem opaque material included in the weight of the non transparent one and inclusions are the usual starting place of future fractures if my broken stones are any indication. Virgin Valley Nevada is known for its black crystal specimens which are not dyed and are completely natural and lots rarer in the collectors market from not being mined due to the reputation earned or not. They don't dry big or even at all too much, but some do which keeps almost all the great material as wet specimens and not lumbered into possible gemstones for sale.

[mick]

Crystal Opal is very under rated.
Its hard to photograph, looks fragile, but gives the most bang for buck IMHO.
Black Opal, esp LRB is very over priced. 30,000 a carat in places for a 1 carat Opal? cmon.

I see some LRB say for 10k and the back is almost 1/3 inch thick but the face only 1mm thick???
I dont see any discount for the potch in these gems.
With Black Opal, you usually only get one depth of color, with crystal you get many.
Black opal, very dense, no light can come up from underneath.
Crystal Opal, you can manipulate the light with a setting.
Good Jelly opal is as good if not better than crystal.
I think the diff between crystal and black is the density of the spheres but Im no xpert.
Crystal sitting on black potch is different to black opal on black potch.
I think if I wanted a black Opal for show, a doublet is the go.
You get an Opal that looks as good as a solid if you get a good one.

[Shea_O]

So what makes an opal black is iron sulfide sitting in between the silica “beads” that are all stacked up. The iron sulfide is an excellent energy-sink, it wants electrons. So when light passes into a black opal, what light escapes (by directly interacting with the silica bonds) comes out as flashes of color and what light doesn’t escape has been absorbed by the iron sulfides. The stone is black because the iron sulfides cause an absence of color - the light is swallowed up by the stone. I like to think of it like a black hole sucking up light and not returning any information - hence the black.

White opal has iron oxides between the silica, which makes the stone look white.

Crystal opal is silica with so few iron sulfides or iron oxides (or a very low concentration of any kinds of inclusions between the silica) that the light mostly passes through the stone unhindered, hence the transparent nature. An opal with absolutely no inclusions would be clear like the glass in a window. I suspect that iron sulfide has beneficial side effects relating to overall stability of an opal. Iron oxide as well. High intensity light is known to crack opals and I believe this is because without enough inclusions - aka “electron hungry” molecules - the photons can break silica bonds, leading to microfractures and larger fractures. Electron hungry inclusions help opal dissipate the energy depositing into the stone, keeping it more stable than it would be if no inclusions were between the silica beads.

So what is a black crystal opal? Its just a black opal with such a low concentration of iron sulfide that you get both effects of both transparency (no light-iron sulfide interactions) and opacity (light is interacting with the iron sulfides and gets absorbed).

The Indonesian black opals for example have such high iron sulfide concentration that it interferes with the POC and the natives have to cook it in baby oil to remove some of the iron sulfides to allow greater interaction of light within the stone.

[Artfldgr]

The Indonesian black opals for example have such high iron sulfide concentration that it interferes with the POC and the natives have to cook it in baby oil to remove some of the iron sulfides to allow greater interaction of light within the stone.

that would make them lose color... no?
opals dont usually respond to heat well given their main medium is the silica AND WATER

just asking...

[mick]

So what makes an opal black is iron sulfide sitting in between the silica “beads” that are all stacked up. The iron sulfide is an excellent energy-sink, it wants electrons. So when light passes into a black opal, what light escapes (by directly interacting with the silica bonds) comes out as flashes of color and what light doesn’t escape has been absorbed by the iron sulfides. The stone is black because the iron sulfides cause an absence of color - the light is swallowed up by the stone. I like to think of it like a black hole sucking up light and not returning any information - hence the black.

White opal has iron oxides between the silica, which makes the stone look white.

Crystal opal is silica with so few iron sulfides or iron oxides (or a very low concentration of any kinds of inclusions between the silica) that the light mostly passes through the stone unhindered, hence the transparent nature. An opal with absolutely no inclusions would be clear like the glass in a window. I suspect that iron sulfide has beneficial side effects relating to overall stability of an opal. Iron oxide as well. High intensity light is known to crack opals and I believe this is because without enough inclusions - aka “electron hungry” molecules - the photons can break silica bonds, leading to microfractures and larger fractures. Electron hungry inclusions help opal dissipate the energy depositing into the stone, keeping it more stable than it would be if no inclusions were between the silica beads.

So what is a black crystal opal? Its just a black opal with such a low concentration of iron sulfide that you get both effects of both transparency (no light-iron sulfide interactions) and opacity (light is interacting with the iron sulfides and gets absorbed).

The Indonesian black opals for example have such high iron sulfide concentration that it interferes with the POC and the natives have to cook it in baby oil to remove some of the iron sulfides to allow greater interaction of light within the stone.

I have a piece of crystal Opal like that, It is full of color but when you put it on a sheet of paper, it is totally transparent and slightly magnifies whats under it. Ive only ever had the one piece like that.

[SwordfishMining]

I was under the impression the Indonesian opal had to be cooked in oil to replace the lost water and to wet the look.

[Shea_O]

The Indonesian black opals for example have such high iron sulfide concentration that it interferes with the POC and the natives have to cook it in baby oil to remove some of the iron sulfides to allow greater interaction of light within the stone.

that would make them lose color... no?
opals dont usually respond to heat well given their main medium is the silica AND WATER

just asking...

You’re right in the sense that a very precious or valuable opal you wouldn’t want to subject to high heat/extreme heat fluctuations because of the risks involved, but not all opal is made equal by nature. Some opal is made well enough, or has a certain composition of inclusions that you could get away with heating the stone and it won’t crack/bust into pieces on the spot. Lots of the indonesian black opal falls into this category. Mostly the oaplized wood. A lot of the wood opal is what the natives are cooking to improve visuals - these pieces of wood opal are often heavily saturated in iron sulfides and mineralized wood. Check out what indonesian laser opal looks like and you’ll see what I mean. All of the mineral inclusions as well as the iron sulfide are enabling the opal to withstand the cooking. This kind of opal is a hell of a lot different from your virgin valley material though. Different kinds of wood first off. Although if you know of the youtuber “Mining America”, He has uploaded videos of using one of the indonesian cooking processes on Virgin Valley opals and surprisingly the VV opal survived (at least for the duration of the video, I can’t speak to those stones current state). You might be surprised what opals from around the world can tolerate.

Also I have noticed that the cooking methods used by the Indonesians can vary. Some people do a dry cook and then introduce oil and some cook the opals in a roiling oil bath. If you watch many videos of the oil bathes you can see the blackness - the iron sulfides- mixing into the oil as it cooks and making it dark like ink spreading in water. Also Indonesia is a country whose populous is almost entirely muslim and to be completely honest not much importance is placed in science there. A lot of the folks cooking their opals may be doing it because it’s the accepted norm there. It suits the needs of the natives and they sell it to eachother without concern. Take that same oil cooked opal and try to sell it across the world and you start getting a lot of concerned people. The opal industry has a lot of shady people and there are no industry standards, so what worka for the Indonesians might not be acceptable or common practice to others.

I was under the impression the Indonesian opal had to be cooked in oil to replace the lost water and to wet the look.

Not all Indonesian opal is the wood opal that is often so saturated in iron sulfide that it looks pitch black. That’s what usually gets cooked. The indonesians have crystal opal and fire opal (they call it tea opal) and that is every bit as stunning and precious as other opals from around the world and that material doesn’t need cooking. They call crystal opal with POC “kalimaya” aka the good **** lol. As far as cooking the opal in oil to replace water/wet the look I cannot speak to this yet (not enough talking to my connections over there yet). There may not be as much logic going into most stones being cooked as there is “this is how I was told to do it”. There isn’t a whole lot of industry in Indonesia, their currency is horribly inflated (one USD= about 12,000 of their IDR’s / rupees) and so a lot of people turn to crafts for money and mining opal has become a more recent way of trying to make a buck. No offense to the hard working people of Indonesia but how do we know what level of education most people crafting opals attain over there? Is science mandatory in their public education? For indonesians, cooking their opal in oil seems perfectly fine and normal and what they tell eachother to do. I have to actually request that my sources NOT cook the stones or place them in oil because it’s just an automatic thing there unless it’s kalimaya.

EDIT: I feel like I should add that the only reason I bring up science is because I do not know if the Indonesians know WHY cooking their opals helps improve POC. I believe among many possible reasons it’s because the hot oil bath removes iron sulfides. Whether the Indonesians know about this detail I do not know.

[Artfldgr]

thanks for taking the time

buy the way, the last piece that would have sold as my account was killed in the middle of the deal
was a lighting ridge opal which is completely clear... you cant see anything.. just a small slightly foggy glass
when you do put it in the sun, you cant see through it any more, it lights up in a pattern

so inside its boring... not enough to get it going
outside, its a completely different stone and would be noticed for how different it is in and out

My wife is indonesian, we have some opals
thanks... (i have a lot more really good eithiopian. and my wife recently did her first diamond trade... someone needed a ring and she was able to navigate the whole thing from obtaining a really good gem cheap (even putting aside someone else!!!), and getting it set for a fee in a setting cheap... allowed the young couple to have a ring that was more than otherwise... )

[SwordfishMining]

That was a disappointment. I sold a stone at great discount for what id ever sell it for in an auction and quit while i was behind. I was showing my friends the "sleepy black crystal" i found last week and they pointed out no, it was so bright of contra luz it was showing poc back out the small end from the reflection inside. It was the first time id looked at it since throwing it in to soak after finding. Didnt find much opening day (Tailings at Rainbow ridge - 2 days late due to rain) The people with the piles found opal as far as i saw and i found a few both on the surface to fracture seal and helped my SIL go thru his pile. Did find a striking crystal nodule for him but his buddies got the better pile of the two. They all got color. Heard somebody else got a real nice one out there in the other piles and lately he has been working 1-2 hours at closing to dome up the opals people want presentable. Some people are paranoid and slide gem logs into 5 gal buckets and nobody sees them as is their right at any of these mines.