suposiite

Suposiite is a rare calcium‑magnesium silicate mineral first described in 1926 by Russian geologist M. V. Nefedov. The mineral occurs as large, grayish‑green fibrous crystals in a few metamorphic pegmatites in the Ural Mountains. Its chemical formula is Ca4Mg(SiO4)3(OH) and it crystallises in the orthorhombic system. The crystal habits are typically elongated fibrous aggregates or prismatic fragments with a perfect cleavage along the [010] direction. On the Mohs scale, suposiite has a hardness of 4.5 to 5. It shows a refractive index of 1.586–1.588, making it optically biaxial. When exposed to dilute acids, the mineral effervesces slowly, indicating a small amount of carbonate impurities.

The name “suposiite” is derived from the Latin word *supo*, referring to its discovery near the site of the ancient town of Supo in the Ural region. Though its geological occurrence is limited, suposiite has attracted interest as a potential phosphate‑bearing analogue of the silicate group; however, no commercial applications have emerged. The mineral is primarily of academic interest, and small amounts are occasionally sold to collectors of rare mineral specimens.

Suposiite has been documented in only a handful of occurrences worldwide, with the most complete specimen housed in the Russian Museum of Mineralogy, St. Petersburg. Research into its crystal chemistry suggests that it may represent a transitional phase between orthorhombic silicates and carbonate‑bearing metaphosphates. Further study is needed to determine its potential use in materials science or geochemical modelling.