Boron - Kern County California, USA — Photo: Pacific Museum of Earth from Canada · CC BY-SA 2.0
Probertite
Probertite is an IMA-recognized mineral species in the borate class, with the chemical formula NaCaB₅O₇(OH)₄·3H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/c).
Key properties: Mohs hardness 3; specific gravity 2.13–2.14; typically white or colorless or yellow; white streak; Vitreous, may be satiny luster; optically biaxial.
IMA symbol Pbr, grandfathered status — known before the IMA’s founding, named in 1929.
Found in lake-bed deposits, the boron supplied by hydrothermal spring activity; may be an ore of boron.
It is found associated with Kernite, colemanite, ulexite, borax.
The mineral was named to honor Frank Holman Probert (1876–1940), Dean of the Mining College, University of California, Berkeley, California, USA, who provided the first specimens.
Collections: Collector Favorites, Rare & Remarkable.