Diaspore - Encyclopedia

    Class : Oxides and hydroxides
    Subclass : Hydroxides and hydrates
    Crystal system : Orthorhombic
    Chemistry : AlO(OH)
    Rarity : Rare

Diaspore is a mineral of aluminous metamorphic rocks : clays, schists, limestone-clay, and bauxites ; in the latter type it can be associated with corundum. Its name comes from the Greek diaspora (dispersion), in reference to its fracturing by heating. The diaspore is scattered grains, lamellar masses, foliated and small scales. It is usually cryptocrystalline and compact. The developed crystals are rare, most of the time prismatic, very elongated, flattened and often striated longitudinally. The diaspore is transparent to translucent, usually colorless, white to gray, occasionally colored in purplish to purple, greenish or yellowish gray. The manganiferous varieties are red to pink, while the pink-green color-change variety is called "zultanite". The diaspore is with the böhmite and the gibbsite one of the essential constituents of the bauxites, extracted like aluminum ore and for the manufacture of refractory materials. It should also be noted that since 2016 the diaspore is widely exploited in Turkey as a jewelery gemstone, its properties and hardness this 6.5 to 7 being quite correct for this use.

3.29 ct diaspore from Turkey
2.48 ct diaspore from Turkey
Twinned diaspore from Turkey
Twinned diaspore from Turkey

Diaspore in the World

The best samples of diaspore come from Turkey (Menderes and Mugla). In these two deposits the purple-gray crystals can reach 20 cm and are commonly of gemmy quality. Beautiful pink-red to purple crystals, sometimes grouped in rosettes, have been found in several manganese mines in Postmasburg District, South Africa. The Russian Urals (Mramorskoye), Massachusetts (Emery Mine) and the Dilln mine (Slovakia) delivered good centimetric crystals of various colors.

Diaspore in France

In France, the diaspore was only reported in cryptocrystalline microcrystals in Chantel (Haute-Loire), the Chizeuil mine (Saône-et-Loire), Costabonnes (Pyrénées-Orientales) and Mas-Rouge (Bouches-du-Rhône).

Twinning and special forms

Diaspore twinned on {021}, with a reentrant angle of about 60°, producing heart-shaped twins, V twins (main photo) or pseudohexagonal aggregates, normal to the pseudhexagonal axis a[100]. On {061} twinning is uncommon.

Fakes and treatments

No fake registered for this mineral species.

Hardness : 6.5 to 7
Density : 3.38
Fracture : Conchoidal
Streak : White

TP : Translucent to transparent
IR : 1.682 to 1.752
Birefringence : 0.048
Optical character : Biaxial +
Pleochroism : Strong
Fluorescence : Sometimes yellow

Solubility : Hydrofluoric acid

Magnetism : None
Radioactivity : None