"Store Didoni" Collection, Macherio (MB)

Typically found in Madagascar (famous for its blue geodes), the United States (Clay Center, Ohio), and Italy (Sicily, associated with sulfur deposits), it is the primary strontium mineral. It forms primarily in sedimentary environments, through evaporitic precipitation in shallow marine basins or as diagenetic cement in limestones and clays, or hydrothermally in geode cavities associated with carbonate rocks. It crystallizes as transparent or translucent tabular prisms, typically pale blue in color (due to lattice defects) but also colorless or white. Hardness 3–3.5 on the Mohs scale, high density (3.95–3.97 g/cm³), perfect cleavage.

An important industrial mineral as a source of strontium (used in fireworks, magnets, and screen glass); highly prized by collectors for its blue color and transparency, especially in Malagasy geodes; fragile due to its cleavage, it requires careful handling.