FMF - Friends of Minerals Forum, discussion and message board

[Pete Richards]

In a collection that I am helping to curate there are two lots of "hexagonal" plates that appear to belong to the same locality. Both are labeled aragonite. One is labeled "Red Mountain". The other is labeled "Wyoming?"

These crystals have a thinner aspect than typical aragonite twins, and the edges tend to be beveled, which is not typical.

There is one reference in Mindat to aragonite from Red Mountain in Wyoming, and it is for aragonite pseudos after hanksite. There are no images.

A search of all aragonite images in the USA in Mindat produces only one image that appears similar, and it is for Albany County, New York!

The five specimens are shown here. The largest is about 3 cm across.

Do these specimens ring a bell for anyone? I'd love to have a credible locality for them.

[Tom Tucker]

Pete, those aragonite crystals are from a locality now in the Big Horn National Recreation Area - easy to access, easy to collect, but forbidden those days. I collected mine about 30 years ago, when, I think, the recreation area literature including rockhounding as a recreation.
The crystals occur in Triassic red beds, and there are similar localities in New Mexico, and I think, Colorado, also in red beds. I can pinpoint the locality for you, but I'd be hesitant to post the locality on a website - too easy to collect, and forbidden. I think there are also similar aragonite twins from similar red beds - in Spain.
I've always been curious about the twinning. The pseudo hexagonal forms are easily seen, but it seems to me that there are also clusters intersecting each other at maybe 45 degrees on the pedion forms. I'll try to find one to demonstrate. Tom

[Kevin Conroy]

These were once referred to as "Indian money" aragonite, but I haven't heard this term used for quite a while. However, if you search for this term on Google you'll see several images.

[Michael Shaw]

Pete,

I concur with Tom as to the location of your aragonite trillings. There is another Wyoming location that produces these near Tie Siding, Wyoming, but I've never seen the beveled edges on those pieces. Nearly identical specimens come from Yeso, Baca County, New Mexico as shown below.

Michael

[James Catmur]

Some of the Spanish localities are in the province of Aragon (but in a series of other provinces too). The locals where I used to collect them call them torres - towers

James

[Pete Richards]

Thanks for all the suggestions. Don't stop now, if you have an opinion and have not offered it.

Michael, from what little of the Tie Siding material, I agree that bevels are lacking, and they are a conspicuous part of "my" samples. You sent an excellent example from a New Mexico location, so why do you concur with Tom's locality in the Big Horn?

Kevin's suggested search led ultimately to a Weinrich page at https://www.weinrichmineralsinc.com/products/calcite-after-aragonite-1502642.php that shows specimens from a Monolith Portland Midwest Company prospect in Albany County, Wyoming that also looks pretty similar. Any comments about this one, anyone?

In general, these crystals seem enigmatic to me. All of the other undoubted aragonite trillings I have seen are more prismatic, and I do not understand the bevels as a form on aragonite, though I'm sure it's possible.

It is suggested that these are actually pseudomorphs of calcite after aragonite. The texture of mine is certainly consistent with pseudomorphy, but that does not prove that they are calcite.

I look forward to more ideas! Thanks!

[Michael Shaw]

Pete,

The reason for my agreeing with Tom on the location was because I have seen specimens from the area Tom mentioned. The location given was Lovell, Wyoming which is in Big Horn County. Mindat has images of 3 specimens from that area, but none show the beveled edges that your specimens have, and honestly I can't remember whether the ones I saw years ago did either. The ones shown on Mindat look very similar to the pieces from Tie Siding, Albany County, Wyoming. I have included a photo of these. The label that came with my specimens listed them as calcite ps. after aragonite. I noticed that Mindat lists 2 of the 3 from Lovell as dolomite pseudos after aragonite, while the 3rd piece is listed as a calcite pseudomorph after aragonite. I have never seen any pieces from Tie Siding with beveled edges.

I have to admit that your specimens most closely resemble the ones I have from Yeso, New Mexico. Hope this helps.

Michael