Ammonioborite

ammonioborite

larderellite

sassolite

pentaborate

Images

Formula: (NH4)3B15O20(OH)8.4H2O
Hydrated pentaborate, paramorph of larderellite
Crystal system: Monoclinic
Specific gravity: 1.765 measured, 1.76 calculated
Streak: White
Colour: White; colourless in transmitted light
Luminescence:
Solubility: Slowly and completely soluble in cold water
Environments

Hydrothermal environments

Localities

The type locality is Larderello, Pomarance, Pisa Province, Tuscany, Italy. The region of Larderello has experienced occasional phreatic eruptions, caused by explosive outbursts of steam trapped below the surface. The water is contained in metamorphic rocks where it is turned to steam, which is then trapped beneath a dome of impermeable shales and clay. The steam escapes through faults in the dome and forces its way out in the hot springs. It possesses a dozen explosion craters, 30 to 250 m in diameter.
Larderello now produces 10% of the world's entire supply of geothermal electricity, amounting to 4,800 GWh per year and powering about a million Italian households. Its geology makes it uniquely conducive to geothermal power production, with hot granite rocks lying unusually close to the surface, producing steam as hot as 202°C.
Contrary to popular belief, Larderello is not a volcano, as no eruptions of magma have occurred there at any point in history.
Ammonioborite is granular, white and lustrous, forming a compact mass with sassolite and associated with larderellite (Mindat).
Ammonioborite from Larderello - Image

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