Diaspore

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Diaspore
Diaspore-Margarite-rare-09-05b.jpg
General
CategoryOxide mineral
Formula
(repeating unit)
α-AlO(OH)
Strunz classification4.FD.10
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPbnm
Unit cella = 4.4007(6) Å
b = 9.4253(13) Å
c = 2.8452(3) Å; Z = 4
Identification
ColorWhite, pale gray, colorless, greenish gray, brown, pale yellow, pink, purple; may exhibit color change
Crystal habitPlatey, elongated to acicular crystals; also stalactitic, foliated, scaly, disseminated and massive
TwinningForms heart shaped twins on {021} or pseudohexagonal aggregates
Cleavage{010} perfect, {110} distinct, {100} in traces
FractureConchoidal
TenacityVery brittle
Mohs scale hardness6.5 - 7
LusterAdamantine, vitreous, pearly on cleavage faces
DiaphaneityTransparent to translucent
Specific gravity3.1 - 3.4
Optical propertiesBiaxial (+)
Refractive indexnα = 1.682 - 1.706 nβ = 1.705 - 1.725 nγ = 1.730 - 1.752
Birefringenceδ = 0.048
PleochroismStrong
2V angleMeasured: 84° to 86°, Calculated: 80° to 84°
Dispersionr < v, weak
FusibilityInfusible
SolubilityInsoluble
Other characteristicsDecrepitates releasing water in closed tube on heating
References[1][2]

Diaspore /ˈdəspɔːr/, also known as diasporite, empholite, kayserite, or tanatarite, 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.[3] 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.[4]

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.[4]

Diaspore, along with gibbsite and boehmite, is a major component of the aluminium ore bauxite.[2]

It was first described in 1801 for an occurrence in Mramorsk Zavod, Sverdlovskaya Oblast, Middle Urals, Russia. The name, which was coined by René Just Haüy,[5] is from the Greek for διασπείρειν, to scatter, in allusion to its decrepitation on heating.[1]

Csarite, ottomanite, and zultanite are trade names for gem-quality diaspore (also known as Turkish diaspore) from the İlbir Mountains of southwest Turkey.[6]

References[edit]

  1. ^ a b Handbook of Mineralogy
  2. ^ a b Klein, Cornelis and Cornelius S. Hurlbut, Manual of Mineralogy, Wiley, 1985, 20th ed. p.318 ISBN 0-471-80580-7
  3. ^ "The Mineral diaspore". minerals.net. Retrieved June 10, 2014.
  4. ^ a b  One or more of the preceding sentences incorporates text from a publication now in the public domainSpencer, Leonard James (1911). "Diaspore". In Chisholm, Hugh. Encyclopædia Britannica. 8 (11th ed.). Cambridge University Press. pp. 168–169.
  5. ^ Spencer 1911.
  6. ^ 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