BöhmiteAlO(OH)c 2001-2005 Mineral Data Publishing, version 1

Crystal Data: Orthorhombic. Point Group: 2/m 2/m 2/m. Rarely as tabular to stout
prismatic crystals, to 2 mm, showing {001}, {110}, {101}, {111}, {221}, and in groups; commonly
extremely fine-grained, in pisolitic aggregates or disseminated.
Physical Properties:
Cleavage: {010}, very good; {100}, well-developed; {001}, poor.
Hardness = 3.5 D(meas.) = 3.02–3.05 D(calc.) = [3.08]
Optical Properties: Semitransparent. Color: White, pale grayish brown; colorless in thinsection. Streak: White. Luster: Vitreous, pearly on {010}.
Optical Class: Biaxial (+). Orientation: X = c; Y = b; Z = a.
α = 1.644–1.648
β = 1.654–1.657 γ = 1.661–1.668 2V(meas.) = 74◦ –88◦
Cell Data:

Space Group: Amam. a = 3.693(1)b = 12.221(2)c = 2.865(1)Z=4X-ray Powder Pattern: Huruni Peak, New Zealand.
6.11 (100), 3.15 (60), 2.347 (60), 1.862 (20), 1.850 (20), 1.308 (15), 1.661 (10)Chemistry:
SiO2TiO2
Al2 O3Ga2 O3(1)2.1181.600.05

(2)
0.76
0.03
83.84

Fe2 O3MgO
CaO
H2 O

(1)
0.58
0.26
15.31

(2)
0.53
0.02
0.08
[15.05]

Total
99.91
[100.31](1) Vishnevy Mountains, Ural Mountains, Russia; corresponds to Al0.98 [O0.96 (OH)1.04 ]Σ=2.00 .
(2) Huruni Peak, New Zealand; by electron microprobe, H2 O calculated from stoichiometry;corresponds to Al0.98 Si0.01 O(OH).
Polymorphism & Series:

Dimorphous with diaspore.

Occurrence: Formed from aluminosilicates during tropical weathering, commonly a major
constituent of bauxites, laterites, or fireclays; a late product of low-temperature hydrothermal
decomposition of corundum, nepheline in nepheline pegmatites, syenites, or ocean-ridge basalts.
Association: Kaolinite, gibbsite, diaspore (bauxites); nepheline, gibbsite, diaspore, natrolite,analcime (nepheline pegmatites).
Distribution: Widespread, but rarely well-crystallized; studied material from: in France, atles Baux, near Arles, Bouches-du-Rhône; at Recoux, Var; and Pérlille and Cadarcet, Ariège. OnMontecchio Maggiore, Vicenza, Italy. At Baratka, Hungary. Crystals from the Tvedalen district
and elsewhere in the Langesundsfjord area, Norway. In the Mandamus complex, 20 km west ofCulverden, New Zealand. In the USA, in the Alberhill clay pits, Riverside Co., California; fromthe Linwood-Barton district, and at the Laurel Creek mine, Rabun Co., Georgia; on Hogback
Mountain, Jackson Co., North Carolina.
Name:

For Johannes Böhm (1857–1938), German geologist, who first studied the species.

Type Material:n.d.

References: (1) Palache, C., H. Berman, and C. Frondel (1944) Dana’s system of mineralogy,(7th edition), v. I, 645–646. (2) Deer, W.A., R.A. Howie, and J. Zussman (1962) Rock-formingminerals, v. 5, non-silicates, 111–117. (3) Sahama, T.G., M. Lehtinen, and P. Rehtijärvi (1973)
Natural boehmite single crystals from Ceylon. Contr. Mineral. Petrol., 39, 171–174. (4) Shelley,D., D. Smale, and A.J. Tulloch (1977) Boehmite in syenite from New Zealand. Mineral. Mag., 41,398–400. (5) Larsen, A.O. (1981) Boehmite from syenite pegmatites in the Oslo region, Norway.
Mineral. Record, 12, 227–230. (6) Hill, R.J. (1981) Hydrogen atoms in boehmite: a single crystal
X-ray diffraction and molecular orbital study. Clays and Clay Minerals, 29, 435–445. (7) Corbató,C.E., R.T. Tettenhorst, and G.G. Christoph (1985) Structure refinement of deuterated boehmite.
Clays and Clay Minerals, 33, 71–75.
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted inany form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior written
permission of Mineral Data Publishing.