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Formula: Na6Mg[B6O7(OH)6]4.10H2O
Hydrated hexaborate
Crystal system: Monoclinic
Specific gravity: 1.905 measured, 1.91 calculated
Hardness: 3½
Streak: White
Colour: Colourless, white
Solubility: Soluble in water
Environments
Sedimentary environments
Hot springs
Rivadavite occurs in sedimentary borate deposits and deposited from
borate-rich hot springs
(HOM).
Localities
At the type locality, the Tincalayu Mine, Antofagasta de la Sierra Department, Catamarca Province, Argentina, the
principal mineral constituent of the deposit is borax but associated with it are
minor amounts of halite and rare borates.
These include kernite, ezcurrite
and mcallisterite. Rivadavite occurs in this association
completely surrounded by massive borax in nearly spherical aggregates measuring
from 1 to 9 cm in diameter. The subparallel arrangement of many of the small crystals gives the nodules a silky
appearance. The nodular masses are composed entirely of aggregates of single crystals with individuals attaining a
maximum length of three mm.
Rivadavite shows three cleavages, two excellent and one poor. The crystals are extremely brittle and tend to
break in splintery fragments. Although the nodules are white, the individual crystals are quite colourless and
transparent with a vitreous lustre
(AM 52.326-335).
Associated minerals include borax and
tincalconite
(HOM).
Rivadavite from the Tincalayu Mine -
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