Hilgardite

minerals

boracite

szaibelyite

volkovskite

Formula: Ca2B5O9Cl.H2O
Hydrated borate containing halogen, hilgardite group
Specific gravity: 2.67 to 2.71
Hardness: 5
Streak: White
Colour: Colourless, light pink; colourless in transmitted light
Environments

Salt domes

Hilgardite is a minor borate mineral in marine evaporite deposits (Webmin, HOM).

Localities

At New Brunswick, Canada, hilgardite is associated with boracite and szaibélyite (HOM).

At the Boulby potash mine, Loftus, North Yorkshire, England, UK, hilgardite occurs with volkovskite (R&M 91-5.434-441), and hilgardite pseudomorphs after boracite have been found (KL p186).

At the type locality, the Choctaw Salt Dome, Plaquemine, Iberville Parish, Louisiana, USA, hilgardite occurs in the salt dome associated with boracite, anhydrite, danburite, dolomite, magnesite, pyrite, hauerite, calcite, quartz, sulphur and gypsum (AM 64.187-195, Mindat, HOM).

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