Identity HelpID help, - "Rainbow moonstone" volcanic glass
Good day!
The samples were gathered at a beach in northern Taiwan, in beach gravel. Volcanic rock in big boulders was present, - basalt, really black, green obsidian in gravel and some nephrite.
We brought the samples to a local gem testing lab, they said over 40% of SiO2 is present and informed us that it's glass.
The origin of these samples is clearly volcanic, - lots of bubbles present, other types of volcanic glass was also locally found. It's not man made, some fragments were merged with native rock.
Scratch test with a good quality kitchen knife - metal streaks are left on the surface, metal does not scratch the sample.
Samples vary in transparency, - from opaque white with black dots dispersed in the samples with or without bubbles to almost completely transparent samples, some specimens contain a lot of bubbles, some are almost clear. When these samples are clear and viewed in the sun, all rainbow colors could be observed. These really look like rainbow moonstones, - some of the samples only have slight hues of blue, some are very vivid green, orange, blue and yellow.
If you allow, my questions are - is this type of volcanic glass common or is it a completely unknown type of volcanic glass? If unknown, what would you recommend to do next to submit or sell these samples to museums, maybe? Could you recommend a testing facility or lab for testing these? Cost of the samples if you can make an approximation?
Sizes vary from 0,1 mm to 60 mm in diameter (dispersed by fragmentation).
Thank you for your professional viewpoints!
Slag glass and slags are quite common in some locations. These are man made. Rocks in glass are not a proof for being natural. Most glass slags have such. Artificial slags and glasses can be found almost everywhere. Even far away from any visible civilization.
The whitish brownish transparent specimens have a minor value as so called sea glass due their uncommon color. But its not much. Some people collect artificial glasses, when it has been rounded by the sea. Thank you for the answer, Alexander! It would be easy to agree if not for the native rock fused with these specimens. Also, as I wrote, tempered steel is not scratching the surface when as using the same knife it's possible to scratch a window glass or a bottle. Why would somebody produce these slags with different opacity, high density and fuse them with rock?!
On the contrary, why do you exclude the possibility of these specimens being natural?
Please take a look at the photos of one of the specimens found and orthoclase:
You can view this image on Mindat here:
https://www.mindat.org/photo-46141.html Keep in mind, that glass has to be contained somewhere. The bricks of the oven may get attached to the glass. And not all kinds of glasses are made intentionally and glass is made of different things. Glass may become crystalline again too.
Just have a look at this thread, here you can find a discussion about glass slags. In the later posts you can see even pieces, which are similar to yours.:
https://www.mindat.org/mesg-55-350039.html Steve, Comparing your last 2 photos: The top one has tiny bubbles in it; the orthoclase has no bubbles in it. Thank you for the reference and the link, Alexander! I looked through the thread and most examples are fakes deliberately produced to fool people. I won't convince anybody by saying that these finds were made where they were made and there is no need, - no money is involved.
I also don't agree that everything suspicious or outside the status quo model of either personal, professional or even academic experience & knowledge should be called glass. Also, I can't agree with you that ovens or kilns would be coincidentally produced of rock, usually refractive materials are used.
And the color of these samples does not look brown to me. More like the same rainbow spectrum that a rainbow moonstone has with strong adularescence.
Despite the opposite opinion I am grateful for your attention and your help, Alexander.
The questions remain unanswered, - if it were not glass, what would be the course of action to establish the natural genesis of these?
Are there any similar minerals or rocks that produce adularescence, rainbow color spectrum and contain bubbles? Moonstone is an obvious analog but it does not contain bubbles, or is it theoretically possible since hardness is almost the same? Thank you for the observation, Alfredo! Yes, in the first post here I noted that either opaque, transparent and translucent or mixed samples do contain bubbles most of the time. Could it be that orthoclase, again, theoretically, contain them?
In this regard, - what would happen to a moonstone at considerable pressure and remelting? As a hypothesis? Well, if a moonstone were melted, it wouldn't be moonstone anymore, it would be glass. So it is possible, after all for these specimens to be of natural origin! ) Alfredo, could you please prove your thesis? If not with chemical formula, what's the logic or chemical dynamics behind the process you proposed? Steve,
On the hardness issue. Glass has a hardness of about 6. A kitchen knife (in fact most knives) have a hardnss of about 5.5. Thus, they won't scratch glass.
Even if you have moonstone, which I doubt, it isn't worth a great amount. I just finished a project in which I was looking at finished jewelry that was fabricated with moonstone. In nearly all cases, each piece of jewelry was less than $50 for the finished piece. Steve, I have not proposed a process, I merely pointed out that if you take a piece of real moonstone and melt it, you have then created a glass, same as you do when melting any kind of silicate rock. It isn't the same mineral anymore, after melting.
I think you'll need to get a chemical analysis of your pieces to see what they are, or what they were made from. With just photos and hardness tests, not going to be enough, unfortunately. The black one is clearly a slag glass. The others COULD be quartz. Alfredo, thank you again. It might be the answer to all my questions, if it were natural stones, that would be it, - remelting in earth core. Yes, I agree, the mineral would be turned into glass. We will redo the chemical test.
Volkmar, - the lower stone is nephrite jade. No, the others are not quartz.
Donald, thank you for the hardness comparison. I don't agree that the price of 200+ carat clear transparent rainbow moonstone would be cheap. However, it's almost clear now, these are thermally altered specimens. 
The first and third photos in this thread are most like likely agate; evident by remnants of conchoidal fracture and faint banding plus the hardness test. These look typically of stream (or beach) worn agate.
In laboratory conditions if you melt moonstone or the feldspar you could manage to regrow very small amounts of small feldspar crystals. All the man-made stuff you find out in the country side is glass, a product of relatively rapid cooling in industrial processes. Where slag is dumped on the ground, it will often include the local rock. Minerals that remelt in the earth core or even at shallow depths (tens of kilometres) recrystallize without air bubbles, and definitely not as glass, because that great laboratory beneath our feet has the temperature, pressure and time to do so. That is why everyone of us here chases these lovely natural works of art.
Air pocket bubbles from rapid cooling, as seen in rocks like basalt, do not occur in minerals and crystals but if you insist they do then it is an extremely rare set of conditions and wouldn't be found commonly in beach gravels and stream sediments. Crystal gas and fluid inclusions are not applicable here as they form through different processes.
When Volkmar said "The black one is clearly a slag glass. The others COULD be quartz.", I am sure he meant the agate is quartz, which it is. Thank you for the expanded reply, Gregg! Very interesting information, I appreciate the time you put in writing this comment.
I can't really insist since I am not a professional in this field, I am just very curious about the origin of these stones. I am not sure if this information is applicable to this case, but the same beach area contains a lot of nephrite pebbles, these too contain bubbles. Besides nephrite bubbles are also visible in volcanic glass, please refer to the photo. The nephrite is tested by the laboratory, it is indeed soft jade.
I probably was to provide this contextual information earlier. This abundance of hard material with gas inclusions logically puts "remelted moonstones" on the same canvas. Or does it not?
These look like typical glass slag, not volcanic glass and surely not nephrite. Hello, Paul! Nephrite has been confirmed by the laboratory, they did a bunch of tests, including specimens with bubbles. Hardness test of soft jade was also positive. Refractive index positive, chemical composition corresponds to nephrite.
I guess we can call it a day with this thread, since there are more questions than answers.. Steve
Are you saying one of those 3 pieces of slag glass has actually been tested as being nephrite jade?
Which one, and by whome? I fully agree with Paul ! And if i were you i would change to another laboratory ;) 
There is no such thing as "soft jade". Both nephrite and jadeite are hard minerals characteristic of high presure metamorphic rocks, and neither of them ever contains macroscopic bubbles. All the pieces in the photos posted this morning look like water-worn man-made glass, and any "laboratory" which identified them as jade is either conning you, or simply incompetent.
Pete N Wayne, yes, that is correct. Darker one.
Thomas, that's an option.
Peter, - soft jade is how nephrite is called in Chinese. I guess I'll need to redo the testing of "nephrite" then return to this thread. Thank you for sharing your ideas, thread is closed. That's exactly the way green bottle glass looks like when it is abraded in beach sand. Nephrite jade never has bubbles. As Thomas said, you need a new laboratory. If anybody would be interested and has testing equipment, I can send "nephrite" and "moonstone" "slags" for analysis if you agree to post results here.
