Diaspore

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Diaspore
Mineraly.sk - diaspor.jpg
Diaspore from Slovakia
General
Category Oxide mineral
Formula
(repeating unit)
AlO(OH)
Strunz classification 04.FD.10
Crystal symmetry Orthorhombic 2/m 2/m 2/m
Unit cell a = 4.4007(6) Å, b = 9.4253(13) Å, c = 2.8452(3) Å; Z = 4
Identification
Crystal habit Platey, elongated to acicular crystals; also stalactitic, foliated, scaly, disseminated and massive
Crystal system Orthorhombic dipyramidal
Twinning Forms heart shaped twins on {021} or pseudohexagonal aggregates
Cleavage {010} perfect, {110} distinct, {100} in traces
Fracture Conchoidal
Tenacity Very brittle
Mohs scale hardness 6.5 - 7
Luster Adamantine, vitreous, pearly on cleavage faces
Diaphaneity Transparent to translucent
Specific gravity 3.1 - 3.4
Optical properties Biaxial (+)
Refractive index nα = 1.682 - 1.706 nβ = 1.705 - 1.725 nγ = 1.730 - 1.752
Birefringence δ = 0.048
Pleochroism Strong
2V angle Measured: 84° to 86°, Calculated: 80° to 84°
Dispersion r < v, weak
Fusibility Infusible
Solubility Insoluble
Other characteristics Decrepitates releasing water in closed tube on heating
References [1][2][3]

Diaspore /ˈdəspɔːr/ is an aluminium oxide hydroxide mineral, α-AlO(OH), crystallizing in the orthorhombic system and isomorphous with goethite. It occurs sometimes as flattened crystals, but usually as lamellar or scaly masses, the flattened surface being a direction of perfect cleavage on which the lustre is markedly pearly in character. It is colorless or greyish-white, yellowish, sometimes violet in color, and varies from translucent to transparent. It may be readily distinguished from other colorless transparent minerals with a perfect cleavage and pearly luster, like mica, talc, brucite, and gypsum by its greater hardness of 6.5 - 7. The specific gravity is 3.4. When heated before the blowpipe it decrepitates violently, breaking up into white pearly scales.

Twinned crystal of Turkish diaspore from Mugla Province, Aegean Region, Turkey (1.8 x .6 x .4 cm)

The mineral occurs as an alteration product of corundum or emery and is found in granular limestone and other crystalline rocks. Well-developed crystals are found in the emery deposits of the Urals and at Chester, Massachusetts, and in kaolin at Schemnitz in Hungary. If obtainable in large quantity, it would be of economic importance as a source of aluminium.

Diaspore along with gibbsite and boehmite are the major components of the aluminium ore bauxite.[3]

It was first described in 1801 for an occurrence in Mramorsk Zavod, Sverdlovskaya Oblast, Middle Urals, Russia. The name is from the Greek for διασπείρειυ, to scatter, in allusion to its decrepitation on heating.[1][2]

Other names for diaspore include empholite, kayserite, tanatarite and spelling variations of these.

Zultanite and Ottomanite are trade names for the gem quality, color change variety of diaspore (also known as Turkish diaspore) from the İlbir Mountains of southwest Turkey.[4][5]

See also[edit]

References[edit]

  1. ^ a b Handbook of Mineralogy
  2. ^ a b Mindat.org
  3. ^ a b Klein, Cornelis and Cornelius S. Hurlbut, Manual of Mineralogy, Wiley, 1985, 20th ed. p.318 ISBN 0-471-80580-7
  4. ^ Mindat - Zultanite
  5. ^ Murat Hatipoğlu, Necdet Türk, Steven C. Chamberlain and A. Murat Akgün, Gem-quality transparent diaspore (zultanite) in bauxite deposits of the İlbir Mountains, Menderes Massif, SW Turkey, Mineralium Deposita, Volume 45, Number 2 (2010), 201-205, DOI: 10.1007/s00126-009-0262-2

 Chisholm, Hugh, ed. (1911). "Diaspore". Encyclopædia Britannica (11th ed.). Cambridge University Press. Public Domain This article incorporates text from a publication now in the public domainChisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press.