By Chisom Ibemere
Thomsonite is the name given to a series of tecto-silicate minerals which belongs to the zeolite group. It was noticed as a mineral prior to 1977 and reclassified in 1997 and given series name, with the mineral species being named thomsonite-Ca and thomsonite-Sr. The initial being the more common variety and a hydrous sodium, calcium and aluminum silicate.
Strontium can substitute for the calcium and the appropriate species name depends on the dominant element. The species are visually indistinguishable and the series name thomsonite is used whenever testing has not been performed. Generally, thomsonite is one of the rarer zeolites.
Thomsonite may be colorless, white, beige, and pink and a perfect cleavage with a Mohs scale hardness of 5-5.5. It has a vitreous, pearly lustre with white Streak. It may be transparent to translucent with specific gravity of 2.23 – 2.29.
Thomsonite occurs together with other zeolite mineral in the amygdaloidal cavities of basaltic volcanic rocks, and often times in granitic pegmatites. It is a rare and desirable member of the zeolite group, which forms in unique and very interesting crystal forms.
It is composed of hydrous sodium calcium aluminium silicate. Thomsonite-Sr contains a domination of strontium over calcium.
Thomsonite is a rare and important collectible zeolite mineral. It may be banded and are often tumbled and polished, and may be used as minor jewelery objects like beads. Other minerals associated with Thomsonite include Prehnite, Laumontite, Natrolite, Chabazite, Analcime, Mesolite, Apophyllite, Chlorite.
Thomsonite ranges from $5 to $20 per gram which is determined by linear fractures, “eyes”, and greenish hues.
