Afghanite - Encyclopedia

    Class : Silicates
    Subclass : Tectosilicates
    Crystal System : Trigonal
    Chemistry : (Na,Ca,K)8(AlSiO4)6(SO4,Cl2,CO3)3 0.5H2O.
    Rarity : Rare

Afghanite is a feldspathoid commonly accompanied by minerals from the sodalite family. It owes its name to its country of discovery : Sar-e-Sang in Afghanistan. It is a mineral of metamorphic limestones in contact with alkaline granites or syenites. It forms elongated azure blue hexagonal prisms ending in pyramids, its microcrystals can also be colorless. Although rare, it is a mineral that finds uses in jewelry and can be cut into faceted gems. Photo © Joe Budd

Afghanite in the World

Afghanite was discovered in 1968 in the lapis lazuli mine of Sar-e-Sang in Afghanistan (province of Badakhchan), which produced the best crystals in the world but also the only ones of macrometric sizes : doubly-terminated prisms to more 6 cm long. It was then described in Germany (Caspar quarry), in Italy (Lazio and Tuscany), in the Pamirs (Tajikistan) and near Lake Baikal in Siberia. These localities, on the other hand, produced only transparent microcrystals.

Afghanite in France

This mineral has not been described in the French underground.

Twinning

No known twin for this mineral species.

Fakes and treatments

Afghanite crystals are often released from their acid matrix, however the acid also etches the Afghanite which then takes on a molten appearance. If the sample is subsequently not properly neutralized, it whitens. Crystals not cleared with acid are rare.


Hardness : 5.5 to 6
Density : 2.6
Fracture : Conchoidal
Trace : White


TP : Translucent
RI : 1.523 to 1.529
Birefringence : 0.006
Optical character : Uniaxial +
Pleochroism : Low
Fluorescence : Orange

Solubility : Hydrochloric and sulfuric acids

Magnetism : None
Radioactivity : None