Class : Silicates
    Subclass : Tectosilicates
    Crystal system : Orthorhombic
    Chemistry : NaCa₂Al₅Si₅O₂₀ 6H₂O
    Rarity : Fairly common

Thomsonite belongs to the group of zeolites, hydrated aluminosilicates consisting of a framework furrowed with channels in which water and large cations are inserted. Thomsonite is one of the most common minerals in this group. Several varieties have been described but remain little used : ozarkite, white from Mount Ozark (Ankansas), lintonite, a pale green transparent ; comptonite from Mount Somma (Italy), etc... Thomsonite is mainly found associated with other zeolites in the cavities of basic magmatic rocks, notably basalts, and in alkaline syenites in the company of nepheline, rarely in contact deposits. White in color, sometimes yellowish or pinkish, brown when it contains impurities, it most often forms spherules or fibroradiated concretions with a vitreous to pearly luster. It was named in honor of Thomas Thomson, Professor of Chemistry at the University of Glasgow (Scotland). Thomsonite rarely occurs in well-formed crystals; they are then elongated and striated according to [001] and flattened on {010} with perfect cleavage.

Main photo : Thomsonite from Papeno'o, Tahiti, French Polynesia © Jean-Vincent Coureau

Twinning on {110} are known and can be cyclic with 4 individuals.

No fakes listed for this mineral species.