DIASPORE
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.
Diaspore in the World
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