Sanidine - Encyclopedia

    Class : Silicates
    Subclass : Tectosilicates
    Crystal System : Monoclinic
    Chemistry : (Ca,Na)AlSi₃O₈
    Rarity : Very common

Sanidine is the alkaline feldspar of acidic volcanic rocks (rhyolites) and intermediates (trachytes) where it commonly forms beautiful white or gray crystals, vitreous, often cracked. It has a more disorderly structure than orthoclase or microcline ; sodium can replace potassium in significant proportions. Sanidine owes its name to the Greek sanidion (board) or sanis (tablet, plate) in reference to the typical shape of its crystals. The crystals come in two different habitus : very flattened crystals with lamellar and elongated parallelepipedal prisms. These two facies commonly present Carlsbad's twinning, the prismatic facies being also frequently mixed by interpenetration. Sanidine has limited use as a gemstone and in the porcelain industry, well-formed crystals are destined for the collection.

Twinning is common for this mineral species especially the Carlsbad's twinning. The twins of Baveno and Manebach are much rarer.

No fake inventories for this species. Assemblages on trachyte matrix are possible.