Twinning in pyromorphite

Mills, S.J., Ferraris, G., Kampf, A.R. & Favreau, G. (2012) Twinning in pyromorphite: The first documented occurrence of twinning by merohedry in the apatite supergroup. American Mineralogist, 97, 415–418.

Abstract

We describe the first documented case of {10-10} twinning by reflection (or by twofold rotation about [100]) or merohedry (class II) in a member of the apatite supergroup. Twinning about [100] had previously been noted for the apatite supergroup but not confirmed. Pyromorphite crystals from Puech de Compolibat, Combret, Aveyron, France, were studied by single-crystal X‑ray diffraction [a = 10.0017(19), c = 7.3413(16) Å, and V = 636.0(2) Å3, in P63/m], where twinning was confirmed with the approximate twin fraction 62:38. Subsequent inspection of the morphology confirmed the nature of the twinning. The pyromorphite crystals are typically elongate and show the faces: (2-1-10), (-2110), (0001), (000-1), (10-10), (-1010), (10-1-2), and (-101-2).

Stuart
So how about a few photos of this and not just an abstract !!
Cheers

Coming!

Edited 1 time(s). Last edit at 02/08/2012 10:44PM by Stuart Mills.

Twinning in mimetite was reported by
Zirkl, E. J. & Stehlik, H. (1985): Neufund von Lavrion - Ein Mimetesit-Zwilling nach (22-43) von Plaka bei Laurion, Griechenland. Lapis 10 (1), 21 (in German),
based on SEM studies (cross-like twins).