What is "quenstedtite"

n. (context mineralogy English) A rare iron sulfate mineral that forms violet or white triclinic crystals.

Quenstedtite is an uncommon iron sulfate mineral with chemical formula Fe(SO)·11HO. It forms violet or white triclinic crystals. Found in oxidized zones of pyrite-rich orebodies, especially in arid climates. It was first reported in 1888 for an occurrence in Tierra Amarilla, Copiapó Province, Atacama Region, Chile and named by G. Linck in 1889 for the German mineralogist F. A. von Quenstedt (1809–1889).