Peanut Obsidian - A Rare Volcanic Glass from Mexico
Who would have guessed that this wild-looking material could be something even closely related to Obsidian? Certainly not me! And I would have thought it even more impossible that we could actually have some of it hidden in the mix of dusty, dirty old rocks from probably one of the very first collections we acquired.
Years ago, Ed forked over a ton of money (at least that’s what I thought at that time) for some big, old, weird-looking machine on this huge metal stand (a fabulous old HighlandPark polisher/grinder for polishing stones). The older gentleman was ready to get out of his old hobby at that time, and along with the polisher came several old wooden ammo cases – full of rocks. Way back then, neither of us could identify many types of rocks, and so, little attention was paid to them. At some point they were just kind of forgotten about – you know, out of sight, out of mind.
Then several years ago we were spring cleaning and opened a couple of the boxes and washed off what was inside. We found an amazing variety of stones, and we were then much more able then to recognize what they were. One of those looked really fascinating to me, though I had no clue what it was. I’d never seen one quite like it. One side was sliced off so you could tell what it would look like inside. It had these weird little nodules on the outside and on the inside once sliced, it looked shiny, kind of glassy. So I selected it to photograph and put up on eBay (at that time, we were doing a lot of eBay, and that was often how I learned what material we had).
I photographed it and was just about to list it as an unknown when I happened to see an article in that month’s Rock & Gem magazine (March 2014, Vol 44 Issue 3) on “Peanut Obsidian”. The article was written by cabochon designer Scott Empey of Gerard Scott Designs. I was sure that was the material I was holding!
It isn’t quite obsidian, but closely related. According to Mr.Empey’s article, it is actually Perlite, a volcanic glass similar to obsidian but it has a higher water content and it is not quite as dense as obsidian. Those beautiful little “peanuts” are spherulites (spherical bodies that generally occur in glassy rocks and frequently have radiating structures like you see in this closeup).
Ed has a few pieces set aside to eventually cut, but he is considering stabilizing them first. He has been more of a purist, preferring to not use any kind of glue or stabilizers but just the natural stone in his creations. The material can apparently be brittle, have fractures and the little “peanuts” can separate from the perlite. So if you are lucky enough to have some of this rare material, and with the stunning potential of a finished cabochon or polished slab, I would certainly recommend stabilizing it first so the amazing creation you have in mind doesn’t just crumble in your hands! There are several techniques that can be found to stabilize a stone before cutting it, including one described in the earlier-referenced Rock & Gem article. I won’t go into those here, but if you’re desperate, reach out and I can forward some tips.
The moral of the story is – if you have ever acquired an old rock collection, or if you come across an opportunity to purchase from someone who has a bunch of old rocks, get to know the varieties. You may discover some real gems hidden in the dust!
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Sources:
Rock & Gem Magazine, March 2014, Vol 44 Issue 3, article entitled “Peanut Obsidian”
EncyclopediaBritancia https://www.britannica.com/science/spherulite
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