FMF - Friends of Minerals Forum, discussion and message board

[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