Cronstedtite Locality: Wheal Jane (Falmouth Consolidated Mines), Baldhu, Kea, Camborne - Redruth - St Day District, Cornwall, England, UK Size : view 1.5 cm — Photo: Didier Descouens · CC BY-SA 4.0
Cronstedtite
A complex black iron serpentine-group silicate named in 1821 for Swedish mineralogist Axel Fredrik Cronstedt.
Intro adapted from Wikipedia (CC BY-SA).
Cronstedtite is an IMA-recognized mineral species in the silicate class, with the chemical formula (Fe²⁺,Fe³⁺)₃(Si,Fe³⁺)₂O₅(OH)₄.
It crystallizes in the hexagonal crystal system (space group R3). It is a member of the Serpentine, Clay structural group.
Key properties: Mohs hardness 3.5; specific gravity 3.34–3.35; Dark olive-green streak; Brilliant luster; refractive index 1.773; optically biaxial.
IMA symbol Cro, grandfathered status — known before the IMA’s founding, named in 1821.
A low-temperature hydrothermal product in ore veins.
It is found associated with Siderite, pyrite, sphalerite, clinochlore, quartz.
The mineral was named to honor the Swedish mineralogist and chemist, Axel Fredrik Cronstedt (1722–1765).