Cronstedtite

Brunita open pit (Brunita Quarry), La Peraleja, Sierra Minera de Cartagena-La Unión, La Unión, Murcia, Spain Copyright © Fontana Gianluca

Chemical Formula: Fe22+Fe3+((Si,Fe3+)2O5)(OH)4
Locality: Pribram and Kuttenberg, Bohemia of Czechoslovakia.
Name Origin: Named for Axel Fredrik Cronstedt (1722-1765), Swedish mineralogist and chemist.

Cronstedtite is a complex iron silicate mineral belonging to the serpentine group of minerals. It has a formula of Fe22+Fe3+((Si,Fe3+)2O5)(OH)4.

It was discovered in 1821 and named in honor of Swedish mineralogist Axel Fredrik Cronstedt (1722–1765). It has been found in Bohemia in the Czech Republic and in Cornwall, England.

Cronstedtite is a major constituent of CM chondrites, a carbonaceous chondrite group exhibiting varying degrees of aqueous alteration. Cronstedtite abundance decreases with increasing alteration.

Physical Properties of Cronstedtite

Cleavage: {001} Perfect
Color: Brownish black, Greenish black, Dark brown, Black.
Density: 3.34 – 3.35, Average = 3.34
Diaphaneity: Transparent to translucent
Hardness: 3.5 – Copper Penny
Luster: Vitreous – Resinous
Streak: dark olive green

Photo

Cronstedtite, Marcasite Locality: Brunita open pit (Brunita Quarry), La Peraleja, Sierra Minera de Cartagena-La Unión, La Unión, Murcia, Spain Copyright © Enrico Bonacina
Locality: Brunita open pit (Brunita Quarry), La Peraleja, Sierra Minera de Cartagena-La Unión, La Unión, Murcia, Spain FOV: 5 mm Copyright © Fontana Gianluca
Locality: Salsigne mine, Salsigne, Mas-Cabardès, Carcassonne, Aude, Languedoc-Roussillon, France Copyright © Germano Fretti
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