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Formula: NaB5O6(OH)4.3H2O
Hydrated pentaborate,
sborgite group
Crystal System: Monoclinic
Specific gravity: 1.713 measured on synthetic material, 1.711 calculated
Streak: White
Colour: Colourless, white
Environments
Sedimentary environments
Volcanic vents
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.
Sborgite occurs as white encrustrations formed from low temperature (32 to 60o C) soffioni
(volcanic vents); it is intimately mixed with thénardite and
borax
(Mindat).
At the Furnace Creek Mining District, Inyo County, California, USA, sborgite was deposited in the arid climate
in surficial debris above weathering borate-bearing veins and in beds of
saline tuffaceous
siltstone. Associated minerals include
halite and thénardite
(HOM).
Sborgite from the Furnace Creek Mining
District - Image
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