Weddellite Locality: Cerchiara Mine, Borghetto Vara, Vara Valley, La Spezia Province, Liguria, Italy Original description: White crust of Weddellite. Field of view 6 mm. — Photo: Leon Hupperichs · CC BY 3.0
Weddellite
Calcium oxalate dihydrate — first found in bottom sediments of Antarctica's Weddell Sea.
Intro adapted from Wikipedia (CC BY-SA).
Weddellite is an IMA-recognized mineral species in the organic mineral class, with the chemical formula Ca(C₂O₄)·2H₂O.
It crystallizes in the tetragonal crystal system (space group I4/m). It is a member of the Oxalate structural group.
Key properties: Mohs hardness 4; specific gravity 1.94; refractive index 1.534; optically uniaxial.
IMA symbol Wed, grandfathered status — known before the IMA’s founding, named in 1936.
Authigenic in bottom muds and in peat sediments; in calcareous lake-bottom sediments; may be formed by reaction of calcite with oxalic acid produced by lichens.
It is found associated with Whewellite, urea, phosphammite, aphthitalite (from bat guano).
The name refers to its first-noted occurrence in the Weddell Sea, Antarctica.