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Formula: B(OH)3
Anhydrous borate
Crystal System: Triclinic
Specific gravity: 1.46 to 1.5 measured, 1.48 calculated
Hardness: 1
Streak: White
Colour: White to grey, occasionally colourless, yellow or brown
Solubility: Soluble in water
Environments
Sedimentary environments
Evaporite deposits
Fumeroles
Sassolite occurs as an evaporite or sublimate around hot spring lagoons and volcanic fumaroles, and
also in bedded sedimentary borate deposits. Associated minerals include
larderellite, santite,
ginorite, probertite,
searlesite, mirabilite,
hieratite, glauberite,
sulphur, realgar,
salammoniac and kalinite
(HOM).
Localities
The type locality is Sasso Pisano, Castelnuovo di Val di Cecina, Pisa Province, Tuscany, Italy.
Sassolite from Sasso Pisano - Image
At the East Coleman Mine, Furnace Creek, Inyo County, California, USA, ginorite
and sassolite were collected in 1954. These two minerals are closely associated, both occurring in soft, white
to pale yellowish brown efflorescent masses in weathered basalt within
50 cm of the surface; the underlying altered basalt contains veins of
colemanite and is associated with
colemanite-bearing limestone.
The ginorite occurs in white pellets which average about 1 to 2 mm in diameter
and are embedded in a pale yellowish brown matrix of sassolite and
clay. In this matrix pearly sassolite plates as much as 1 mm in
diameter are present. Minute grains of celestite and of
quartz are sporadically distributed in the efflorescence
(AM 42.56-61).
At The Geysers, West Mayacmas Mining District, Sonoma County, California, USA, in a group of minerals collected from
this area, one specimen consisted of a matte of tiny transparent flakes of sassolite. The same group of specimens
contained boussingaultite and
mascagnite
(AM 43.1204-1205).
At Steamboat Hot Springs, Steamboat Springs Mining District, Washoe County, Nevada, USA, sassolite was found in
crystalline incrustations on the roof and walls of a partly enclosed large hole in a siliceous sinter terrace. The hole
had formerly been filled with hot water and was perhaps an extinct geyser pool. Lowering of the water table had drained
the pool so that in 1941 it was relatively dry, but steam issued from small vents in the floor. The sassolite
seemed to be forming at the time by evaporation of droplets of water condensed from the steam. The mineral occurred in
very thin, transparent, curved, cellophane-like flakes of small size. Perhaps some were as large as 2 mm across
(AM 43.1204-1205).
At the Norris Geyser Basin, Park County, Wyoming, USA, specimens were collected that consisted predominantly of
water-soluble sulphates and other solfataric and hot spring deposits. One sample consisted of small nodular growths of
halite intimately intergrown with at least three unidentified minerals.
Sassolite occurred in tiny, curved, transparent flakes coating the other minerals
(AM 43.1204-1205).
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