Cronstedtite is a complex iron belonging to the serpentine group of minerals. Its chemical formula is Fe2+ 2Fe3+ (Si,Fe3+ O 5)(OH) 4.
It was discovered in 1821 and named in honor of Swedish mineralogist (1722–1765). It has been found in Bohemia in the Czech Republic.
Cronstedtite is a major constituent of CM chondrites , a carbonaceous chondrite group exhibiting varying degrees of aqueous alteration. Cronstedtite abundance decreases with increasing alteration.