Diaspore
| Diaspore | |
|---|---|
 Diaspore from Slovakia |
|
| General | |
| Category | Oxide mineral |
| Chemical formula | α-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 | 3.2 - 3.5 |
| 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 is a native aluminium oxide hydroxide, 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.
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 is a gem quality form of diaspore from Turkey.[4]
[edit] See also
[edit] References
- ^ a b Handbook of Mineralogy
- ^ a b Mindat.org
- ^ a b Klein, Cornelis and Cornelius S. Hurlbut, Manual of Mineralogy, Wiley, 1985, 20th ed. p.318 ISBN 0-471-80580-7
- ^ Mindat - Zultanite
Chisholm, Hugh, ed (1911). "Diaspore". Encyclopædia Britannica (11th ed.). Cambridge University Press.
This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press.
