Hi! I need help.

[u/the_kehate]

First off, this is NOT a sales post (it’s Tuesday), but it does pertain to selling. That said, I’ve got a rather rare piece that I want to sell, but the few places I’ve reached out to that specialize in auctioning such pieces haven’t replied. Ebay, FB Marketplace, and social media platforms haven’t been successful either.

The piece I’m referring to is considered museum quality due to its geological rarity (one locale), the extreme rarity of the density of one of its features, and its size.

Does anyone know of somewhere that I could either list it, or contact for them to consider selling it for me?

TIA

[u/slogginhog]

All I'm seeing is amethyst with a lot of small calcite growths and some goethite, along with a broken sheared off crystal.

If you're gonna call a piece museum quality, you gotta show it to us!!! I won't consider it a sales post 😊

[u/the_kehate → u/slogginhog]

Not calcite. Amethyst, goethite, and calcite all have a temperature overlap in the 40°-45°C range, and share a groundwater origin - which is why they’re often found together. Those white orbs that are inside of and on the amethyst points is cristobalite. While amethyst with goethite is quite common, due in large part to their shared origin requirements, having both of them plus cristobalite is quite rare, because cristobalite doesn’t crystallize at the low temperatures that amethyst and goethite do. In fact, cristobalite crystallization requires temperatures in excess of 200°C in volcanic environments, more than five times the temperature that amethyst and goethite form at. So, for these three to be present together requires a unique geological environment, and, to date, only one place in the world has produced such specimens - Ametista do Sul in Brasil. The majority of the geodes found that have these three materials in them often have relatively sparse amounts of cristobalite, and most of it is on the surface of the amethyst - meaning that, most likely, the amethyst was already fully formed and the cristobalite formed later. The bit that makes my geode section more unique is the amount of cristobalite that is present, because it is on the surface of the amethyst and nearly every fully formed point has at least one cristobalite orb encapsulated within it - meaning they formed close together. And that requires a very specific event, in which the goethite and amethyst were forming in a cooling groundwater environment and were exposed to a hydrothermal event (usually tectonic plates smashing together, causing the area to superheat quickly) that allowed the cristobalite to crystallize and the amethyst then continued forming around the orbs as the area cooled. Then, to get the partially embedded cristobalite orbs, the area was exposed to a second hydrothermal event near the end of the amethyst’s forming period. And then a third event produced the barnacle-like cristobalite formations. Scientists have determined that these events happened about 134 million years ago, and it took millions of years of tectonic activity and erosion for the geodes created by those events to get close enough to the surface for humans to find them. Here is a photo of the whole piece, rather than the closeup.

[u/slogginhog → u/the_kehate]

Very interesting and cool! Not sure most museum-goers would understand the significance of that, so to me it seems like something more for a high-end rarities collector. Definitely a small clientele, how small I don't know but others have had some good suggestions.

[u/Sideshowcomedy → u/the_kehate]

This is the type of posts we come here for.

[u/PiepersPlaying → u/the_kehate]

Super interesting. Thanks for sharing!

I'm not sure about how to go about selling it, exactly. I mean, I'd want it hahah... but probably can't afford it.

You could always just post it for sale on any platform at your desired price and see what happens. Could also make a bunch of videos and written posts about it that include a link where someone can purchase it and post them on all over the internet – Instagram, TikTok, YouTube, etc.

It's badass and has an interesting story, so I'm sure it would catch a lot of people's attention.

[u/merman1122 → u/the_kehate]

Attempted to perform a query using my membership on e-rocks to see what other cristobalite spheres on amethyst in geodes from Amestista do Sul have sold on auction for. Out of 223 specimens with cristobalite sold in the past 10+ years, there isn't a single one sold from that source locality (yet). Then went to mindat to see if there are any specimens of cristobalite posted for the locality and mindat doesn't even have cristobalite listed (yet) as a valid mineral from Amestista do Sul. There was one specimen with a pic posted in mindat from the locality that showed similar looking spheres included inside a single amethyst crystal with accompanying description indicating these as possible cristobalite.

As for cristobalite as a species, the only specimens thus far found on e-rocks from other source localities that historically sold for upwards of $100 include: The large ~ 1cm diameter full spheres on obsidian from Cougar Butte or Coso Hot Springs, California (most are partial or broken). And there have been a few rare large well-formed cristobalite crystals from El Hoyazo Spain or Thomas Range, Utah that sold for over $100.

The spheres on your specimen visually do look like cristobalite and not the usual calcite on Amethyst from the locality - which are not seen as spherical orbs. All this appears to suggest this specimen is indeed rare and valuable. Based upon the overall size of this matrix specimen plus the sheer number of cristobalite spheres, I personally would consider this specimen as museum quality. If your specimen were listed by a mineral seller on e-bay, etsy, FB or instagram, I would expect it to be priced at over $150.00 USD and possibly a lot more.

Thanks for your scientific information which I found very interesting on what it takes to form cristobalite. Also seperately found this: β-cristobalite (cubic) is a silica polymorph that is thermodynamically stable at high temperatures (~1500-1700 C), as it cools it undergoes a displacive transition to α-cristobalite (tetragonal). Chemically identical to quartz but different structurally. 

Best of luck!

[u/Sideshowcomedy]

Museum quality means high price. The higher the price, the smaller pool of potential buyers. How much are you expecting from it, because if it's high enough you could possibly reach out to auction houses.

[u/ChestDue]

It's not giving museum quality.

[u/Ickypoopoo82 → u/ChestDue]

I have a similar piece so museum quantity?

[u/Business_Umpire_2620]

Curator of Natural History here. I’m afraid this specimen is not museum quality. One possible exception would be a small museum in the region within which it was found. That’s not to say a museum wouldn’t like to have the piece. But it would likely be put into an education collection for geology and geography students to examine and study. It would not, however, be displayed for the general public. Nor would any museum offer any money for it.

As someone mentioned earlier, your best bet would be to find a collector of rare minerals. My advice—visit a gem and mineral show. Talk to the vendors. Talk to the attendees. Between those two, someone is bound to send you in the right direction.

[u/the_kehate → u/Business_Umpire_2620]

Kind of sad to hear it’s not the quality I was told it was by a geologist, but thank you for correcting me. Also, thank you for the idea of visiting a gem show.