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). http://www.mindat.org/forum.php?read,9,251700,251700#msg-251700 Sat, 25 May 2013 13:08:57 +0000 Phorum 5.2.15a http://www.mindat.org/forum.php?read,9,251700,255287#msg-255287 http://www.mindat.org/forum.php?read,9,251700,255287#msg-255287 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).]]> Uwe Kolitsch Mineralogical Classification Wed, 14 Mar 2012 16:33:11 +0000 http://www.mindat.org/forum.php?read,9,251700,251812#msg-251812 http://www.mindat.org/forum.php?read,9,251700,251812#msg-251812

© Laurent Gayraud 2011

]]> Stuart Mills Mineralogical Classification Wed, 08 Feb 2012 22:43:15 +0000 http://www.mindat.org/forum.php?read,9,251700,251754#msg-251754 http://www.mindat.org/forum.php?read,9,251700,251754#msg-251754 Stuart Mills Mineralogical Classification Tue, 07 Feb 2012 23:15:05 +0000 http://www.mindat.org/forum.php?read,9,251700,251720#msg-251720 http://www.mindat.org/forum.php?read,9,251700,251720#msg-251720 So how about a few photos of this and not just an abstract !!
Cheers]]> Keith Compton Mineralogical Classification Tue, 07 Feb 2012 11:05:46 +0000 http://www.mindat.org/forum.php?read,9,251700,251700#msg-251700 http://www.mindat.org/forum.php?read,9,251700,251700#msg-251700
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 Mills Mineralogical Classification Tue, 07 Feb 2012 00:36:19 +0000