| Diaspore | |
|---|---|
 | |
| General | |
| Category | Oxide mineral |
| Formula | α-AlO(OH) |
| IMA symbol | Dsp[1] |
| Strunz classification | 4.FD.10 |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H–M symbol: (2/m 2/m 2/m) |
| Space group | Pbnm |
| Unit cell | a = 4.4007(6) Å b = 9.4253(13) Å c = 2.8452(3) Å;Z = 4 |
| Identification | |
| Color | White, pale gray, colorless, greenish gray, brown, pale yellow, pink, purple; may exhibit color change |
| Crystal habit | Platy, elongated toacicular crystals; also stalactitic, foliated, scaly, disseminated, and massive |
| 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 | 6.5–7.0 |
| 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: 84–86° Calculated: 80–84° |
| Dispersion | r <v, weak |
| Fusibility | Infusible |
| Solubility | Insoluble |
| Other characteristics | Decrepitates releasing water in closed tube on heating |
| References | [2][3] |
Diaspore (/ˈdaɪ.əˌspɔːr/) – also calleddiasporite,empholite,kayserite, ortanatarite – is analuminium hydroxide oxide mineral, α-AlO(OH), crystallizing in theorthorhombic system andisomorphous withgoethite. It occurs sometimes as flattened crystals, but usually as lamellar or scaly masses, the flattened surface being a direction of perfectcleavage on which thelustre is markedly pearly in character. It is colorless or greyish-white, yellowish, sometimes violet in color, and varies fromtranslucent to transparent.[4] It may be readily distinguished from other colorless transparent minerals with a perfect cleavage and pearly luster (e.g.mica,talc,brucite, andgypsum) by its greater hardness of 6.5–7. Itsspecific gravity is 3.4. When heated before the blowpipe, itdecrepitates violently, breaking up into white pearly scales.[5]
The mineral occurs as an alteration product ofcorundum oremery and is found in granularlimestone and other crystalline rocks. Well-developed crystals are found in the emery deposits of theUral Mountains and atChester, Massachusetts, and inkaolin at Schemnitz inHungary. If obtainable in large quantity, it would be of economic importance as a source ofaluminium.[5]
Diaspore, along withgibbsite andboehmite, is a major component of the aluminiumorebauxite.[3]
It was first described in 1801 for an occurrence in Mramorsk Zavod,Sverdlovskaya Oblast, MiddleUrals,Russia. The name, which was coined byRené Just Haüy,[6] is from theAncient Greekδιασπείρω meaning "to scatter", in allusion to its decrepitation on heating.[2]
Csarite,ottomanite,Turkizite andzultanite are trade names for gem-quality diaspore (also known as Turkish diaspore) from theİlbir Mountains of southwestTurkey.[7]
One or more of the preceding sentences incorporates text from a publication now in thepublic domain: Spencer, Leonard James (1911). "Diaspore". InChisholm, Hugh (ed.).Encyclopædia Britannica. Vol. 8 (11th ed.). Cambridge University Press. pp. 168–169.