Torrelite is a rare and highly specific mineral that belongs to the calcite group, specifically the aragonite subgroup. It is an enticing combination of calcium, aluminum, and sulfur, with a chemical formula of Ca4Al2(SO4)(CO3)(OH)12·14H2O. The mineral receives its name from the locality where it was originally discovered, Torre di Monte, Italy.
Torrelite typically appears as small, thin, bladed or prismatic crystals that occur in aggregates or clusters. The crystals often exhibit a translucent to transparent appearance with a vitreous to silky luster. The color of torrelite can range from white to light blue, and occasionally greenish. It possesses a brittle tenacity, meaning it is easily broken. On the Mohs scale, torrelite has a hardness of around 3, making it relatively soft.
Significant specimens of torrelite have been found in the pozzolana deposits near Rome, Italy, and other localities including Hungary, Slovakia, and the United States. Due to its limited occurrence and small crystal size, it is considered a collector's mineral.
Torrelite's crystal structure comprises alternating layers of carbonate groups and sulfate groups, with calcium and aluminum cations in between. It forms through the secondary alteration of volcanic rocks, particularly in arid regions where evaporation and alteration processes take place. Torrelite is often associated with other minerals like calcite, gypsum, and sulfur.
