diaspore

1. A white, pearly hydrous aluminum oxide, AlO(OH), found in bauxite, corundum, and dolomite and used as a refractory and abrasive.
2. Botany. See disseminule.

[From Greek diasporā, dispersion, scattering. See Diaspora.]

A mineral form of a mixed aluminium oxide and hydroxide, AlO.OH. See aluminium hydroxide.

Environment

A constituent of emery, and associated with regionally metamorphosed aluminous rock, recycled perhaps from an earlier bauxite. Occasionally in veins with crystals.

Tiny crystals may be in bauxite pisolites. Good crystals are rare and may cover bladed crusts in worked emery deposits. Large gemmy crystals several inches in size (6-7 cm) have been found in Turkey.

Colorless, straw-colored, or pale greenish, blue, violet, pink, or reddish (mangandiaspore); pleochroic in several hues. Luster glassy to pearly on cleavage face; hardness 6Ɖ-7; specific gravity 3.3-3.5; fracture conchoidal; cleavage 1 perfect and 2 minor. Brittle; translucent to transparent.

Hydrous aluminum oxide (Al ₂ O ₃ 85%, H ₂ O 15%), with intrusions of Fe and Mn up to about 5% (mangandiaspore).

Infusible, but decrepitates strongly into pearly flakes. Then gives aluminum test with cobalt nitrate.

The emery environment would suggest diaspore for any colorless orthorhombic crystals found there. It is not at all common.

Although there are many sources, few are noteworthy and until now, diaspore has never delivered on its promise. A new source of spectacular gemmy, straw to violet crystals in Yagatan, Mugla Province, Turkey has inspired this addition. The gemmy Turkish material as been cut into some notable collection stones. Unfortunately the best violet hue lies in the wrong direction for the largest recovery. Good crystals have never been abundant; some of the best came many years ago from Pennsylvania while an emery mine in Chester, Massachusetts, gave crusts of half-inch (1 cm) crystal blades of a pale violet hue. Mangandiaspore is found in coarsely crystalline masses at Postmasburg, South Africa.

Not to be confused with Diaspore (botany) or Diaspora.

This article's citation style may be unclear. The references used may be made clearer with a different or consistent style of citation, footnoting, or external linking. (September 2009)

Diaspore from Slovakia

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.

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

See also

• aluminium oxide
• aluminium hydroxide

External links

• Mindat

This article incorporates text from the Encyclopædia Britannica, Eleventh Edition, a publication now in the public domain.

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