Gaudefroyite Locality: Wessels Mine (Wessel's Mine), Hotazel, Kalahari manganese fields, Northern Cape Province , South Africa ( Locality at mindat.org ) Size: 1.8 x 1.3 x 1.2 cm. A superb cluster of very lustrous Gaudefroyite crystals, some of the best I have ever seen in terms of sharpness and arrangement in thumbnail size. The largest of the well-formed crystals is a full 1 cm tall, and several of the crystals in the cluster are doubly-terminated. It is a full-sized thumbnail, overall. Ex. Charlie Key. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Gaudefroyite
Gaudefroyite is an IMA-recognized mineral species in the borate class, with the chemical formula Ca₄Mn³⁺₃(BO₃)₃(CO₃)O₃.
It crystallizes in the hexagonal crystal system (space group P6_3/m).
Key properties: Mohs hardness 6; specific gravity 3.35–3.5; Vitreous to dull luster; optically uniaxial.
IMA symbol Gfy, IMA status: approved, named in 1964.
An uncommon hydrothermal mineral in manganese deposits.
It is found associated with Marokite, braunite, hausmannite, crednerite, pyrolusite, calcite, quartz, brucite (Tachgagalt, Morocco); barite, calcite, hydrogrossular, manganite, bixbyite.
The mineral was named to honor Abbé Christophe Gaudefroy (1888–1971), French mineralogist who worked in Morocco.