Pale yellow prismatic crystals of the very rare Mg borate mineral wightmanite from Crestmore Quarries, Riverside County, California, United States of America. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY 4.0
Wightmanite
Wightmanite is an IMA-recognized mineral species in the borate class, with the chemical formula Mg₅O(BO₃)(OH)₅·2H₂O.
It crystallizes in the monoclinic crystal system (space group I2/m).
Key properties: Mohs hardness 5.5; specific gravity 2.6; Vitreous luster; optically biaxial.
IMA symbol Wmn, IMA status: approved, named in 1962.
Very rare in contact metamorphosed limestone.
It is found associated with Fluoborite, szaibélyite, dolomite, calcite (Commercial quarry, California, USA).
The mineral was named to honor Randall H. Wightman (1915–1969), Director of Exploration and Mining of the Riverside Cement Co., Riverside, California, USA.