Sassolite

Sassolite
Yellow sassolite
General
Category	Borate mineral
Formula (repeating unit)	H3BO3
Strunz classification	6.AA.05
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
Space group	P1
Unit cell	a = 7.02 Å, b = 7.06 Å c = 6.59 Å; α = 103.65° β = 101.11°, γ = 59.98°; Z = 4
Identification
Colour	White to gray, may be pale yellow from included sulfur or pale brown from included iron oxides; colourless in transmitted light
Crystal habit	As scaly pseudohexagonal crystals; ncrustations; platy; tabular; may be stalactitic
Twinning	Around [001] as twin axis, common
Cleavage	Perfect on {001}, micaceous
Tenacity	Sectile
Mohs scale hardness	1
Lustre	Vitreous to pearly
Streak	White
Diaphaneity	Transparent
Specific gravity	1.46-1.50
Optical properties	Biaxial (-)
Refractive index	nα = 1.340 nβ = 1.456 nγ = 1.459
Birefringence	δ = 0.119
2V angle	Measured: 5°, Calculated: 16°
Solubility	Soluble in water
References

Sassolite is a borate mineral, and is the mineral form of boric acid. It occurs in volcanic fumaroles and hot springs, as well as in bedded sedimentary evaporite deposits.

Its mineral form was first described in 1800, and was named after Sasso Pisano, Castelnuovo Val di Cecina, Pisa Province, Tuscany, Italy where it was found. The mineral may be found in lagoons throughout Tuscany and Sasso. Usually coloured white to gray, it is colourless in transmitted light, and can also take on a yellow colour from sulfur impurities, or brown from iron oxides.