Formula: CaB2O(OH)6.2H2O
Hydrated borate containing hydroxyl
Specific gravity: 2 to 2.03
Hardness: 2½
Streak: White
Colour: Colourless

Sedimentary environments
Metamorphic environments

Pentahydroborite occurs in skarn (Webmin).


At the Shijiang Shan-Shalonggou mining area, Inner Mongolia, China, the mineral deposits occur predominantly in veins of hydrothermal origin in skarn. Pentahydroborite occurs as clusters of platy to wedge-shaped colourless crystals to 12 mm, freestanding on the walls of cavities. Associated minerals include andradite, minor galena and wurtzite, but no other borate mineral has been observed associated with pentahydroborite (R&M 96.5.404)

At the type locality, the Novofrolovskoye B-Cu deposit, Tur'insk, Turya river, Turinsk-Auerbakovsk ore field, Serovsky District, Sverdlovsk Oblast, Russia, pentahydroborite occurs in boron-rich iron ore skarn as small grains associated with andradite-grossular, magnetite, frolovite and szaibélyite (AM 47.1482-1485, Mindat, HOM).

At the Pobrdzhsky Potok & Peskanya deposits, Baljevac na Ibru, Jarandol Basin, Raška, Raška District, Central Serbia, pentahydroborite occurs in in a volcanogenic-sedimentary borate deposit associated with colemanite, howlite, ulexite and studenitsite (HOM).

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