Crandallite

Crandallite is a rare phosphate mineral with the chemical formula CaAl3(PO4)2(OH)5·H2O. It is a member of the crandallite group, which are hydroxyphosphates and hydroxyarsenates of divalent and trivalent cations. Crandallite typically occurs as a secondary mineral in sedimentary rocks and as a weathering product of other aluminum phosphate minerals.

The mineral was first described in 1949 from a deposit in the Thomas Range, Utah, USA, and named in honor of geologist James R. Crandall. It is usually found in nodular or oolitic forms, often appearing as small, rounded grains or aggregates. The color of crandallite can vary from white to gray, yellowish, or even pinkish. It has a dull to vitreous luster and a Mohs hardness of 2.5 to 3.

Crandallite forms under low-temperature and low-pressure conditions, often in arid or semi-arid environments. It is associated with other phosphate minerals such as wavellite, variscite, and turquoise, as well as clays and carbonates. While not economically significant as a primary ore, its presence can indicate specific geological conditions and may be found in association with rare earth elements. Its rarity and specific formation conditions make it of interest to mineralogists and geologists studying sedimentary processes and mineral paragenesis.