FMF - Friends of Minerals Forum, discussion and message board

[Mathias]

Hi all,
I've purchased 2 Amethyst specimen recently. They have strange crystallization unusual in fact. The vendor said he purchased a box of these amethysts and due to bad packing, most were damaged. He said they are found in Jefferson County, Colorado.
Does anyone know a more exact location?
Thanks,
Mathias

[ALshawani]

Nice Amethyst specimen

[John Hodgson]

It looks similar to various specimens I have had from Thunder Bay Ontario.

[Amir Akhavan]

This looks odd.
What does it look from the side and below?

[James Catmur]

I see Fluorite cubes. Could you test the hardness?

[Mathias]

[Amir Akhavan]

Without doubt amethyst, yes, but I wonder if they have been assembled or not.
The crystals are probably from Brejinho das Ametistas in Bahia, Brazil, the "corroded prism and lower edges of the rhombohedral faces are typical. But usually these tips are made of subparallel groups radiating from a common point, here they are chaotically intergrown.

So again: post a photo from the side and the bottom.

[Philippe Durand]

definitively, I see fluorite cubic crystals: no doubt ! one with octahedral faces

if other crystals are amethyst, I guess , that it is a man made specimen

but my opinion it that is all fluorite, with some heavily corroded crystals

hardness test will kill the question.

[Linus]

[Mathias]

Hi here are some photos from the other specimen (I bought 2).

[Jordi Fabre]

Quartz (variety amethyst) as Amir well said. I had some others from Brazil as Amir also said, and even some from Bolivia.

It looks a lot like Fluorite in the images but is not.

[Amir Akhavan]

Sideways and from the back, please. So far it looks natural and not assembled, as I first thought.

A hardness test is not necessary, but it doesn't hurt, of course,

This cannot be fluorite, because the face development violates its symmetry. You see the tips of quartz crystals with very large r and very small z faces.
The z faces are at every other corner, which is not ok for fluorite, and at the corner they should also appear on all three sides, not just one. For example, the symmetry of fluorite would require the z face to be also visible at the tips (and again three of them), which they don't do.

[Amir Akhavan]

I agree with Jordi, could also be from Bolivia.

[Linus]

Amir, I visited your quartz website, very nicely done! It really helps to clarify this situation.

[Joseph DOliveira]

There is a specimen from the Creede Mining District, Colorado posted in mindat that has a similar appearance, unfortunately the picture is not a good quality one. Here is the link:

https://www.mindat.org/photo-376582.html

[Roger Warin]

Hello,
I believe that fluorite and quartz differentiation tests are easy to perform.
There are at Richelle (Liege-B), some quartz crystals whose habit is pseudo-cubic.
This occurs when the rhombohedron r is the dominant crystallographic form.
The rhombohedron differs only very little from that of a perfect cube (respectively 85.2° and 94.8° instead of 90°), the crystals resemble a slightly tilted cube. On this crystal we see the other rhombohedron (z) and the prism (m), very little developed.
This is an opportunity to ask the question (I don't know): when does this inversion of prismatic towards rhombohedral habit occur in quartz?

Note:
This quartz crystal allows me to introduce you to Jean-Luc. After having been president of the Association of Amateur Geologists of Belgium (AGAB) for more than 50 years, I proposed my succession to Jean-Luc Vanhees. He has all the qualities to lead this big club (> 200 members) in a period that promises to be difficult for amateurs.
Personally, I walked through the 20th century in its best temporal window.
And I discovered GIs in September 1944 south of Bastogne.
In the sixties, it was only our quarries to find minerals, but we could easily go there. And also in Idar-Oberstein.
In Belgium, the trade in minerals developed in the 1970s and so did the quality of the specimens.
In the eighties, I bought a beautiful colemanite from Turkey from a German dealer who had exchanged it for a washing machine.
But in those blessed times, Jordi's FMF forum didn't exist!

[Bob Morgan]

This is definitely quartz with pseudocubic terminations - only the three 'r' faces.

Some of the crystals have Dauphene twins side by side. they are smaller crystals in 180 degree opposite orientation. Such is fairly common with white crystals in Keokuk geodes around Southern Missouri and some from Sauerland, Germany.

Recently I saw an amethyst that did that from Uraguay, but it didn't look as strongly purple.

[James Catmur]

I really hesitated mentioning Fluorite and am glad it was corrected. This discussion also explains some Quartz I have collected