On a Crystal of Augelite from California

M. A. Peacock and D. A. Moddle
Associate Professor of Mineralogy, University of Toronto
Ontario Department of Mines.

Summary: A large well-formed crystal of augelite from the andalusite deposit on White Mountain, Mono Co., California, shows the forms c(001), b(010), a(100), j(130), k(120), l(230), m(110), s(210), t(310), r(021), f(201), x(2¯01), n(111), p(221), o(1¯11), with a : b : c = 1·6419 : 1 : 0·6354, β = 112° 2612 ′ (Spencer, in the structural setting); the forms j k l s t p are new or confirmatory. Cleavages (110), (2¯01), also new (001), (1¯01). Spencer's optical orientation is confirmed; Z (acute bisectrix): c = +34 1 2 ° 2V = 52°. The unit cell with a 13·10, b 7·96, c 5·06 Å., β = 112° 26 1 2 ′, contains 4[Al2PO4(OH)3]. The space-group obtained from the morphology by Donnay's law, and independently from the X-ray extinctions, is C2h3=C2∕m, accepting the holohedral class indicated by the absence of pyroelectricity (Martin's method). The X-ray powder spectrum is reproduced and partially indexed.

Mineralogical Magazine; December 1941 v. 26; no. 175; p. 105-115; DOI: 10.1180/minmag.1941.026.175.01
© 1941, The Mineralogical Society
Mineralogical Society (www.minersoc.org)