Sassolite

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.[1]

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	[1][2][3]

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.[3] The mineral may be found in lagoons throughout Tuscany and Sasso.[2] 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.[1]