Thomsonite is a rare and highly collectable member of the Zeolite mineral group, forming unique and striking crystal aggregates. Its color is white, colorless, beige, yellow-orange and pink. It exhibits a vitreous to pearly luster and is transparent to translucent. In addition to being collectable, it also has a surprising role in the gem/jewelry trade; nodules of massive Thomsonite that display beautiful and colorful concentric “eye” patterns are found along the shore of Lake Superior, and are often used as gemstones. Associated minerals include Prehnite, Natrolite, Quartz, Calcite, Stilbite and other Zeolites.
The crystal system for Thomsonite is orthorhombic, its elongated, bladed crystals typically forming tight acicular radiating clusters and sphericules, fans and tufts. These aggregates are commonly ball-shaped and “spiky”, often found in interconnected masses, cavities and vugs.
Quality specimens of Thomsonite are found in limited localities, including Czech Republic, Denmark, Germany, India, Portugal, Russia and the USA (Minnesota, New Jersey).