Mesolite

Mesolite
Mesolite from Bombay collected in the 18th century by Dr John Hunter
General
Category	Tectosilicate minerals, zeolite group, natrolite subgroup
Formula	Na2Ca2Si9Al6O30·8H2O
IMA symbol	Mes[1]
Strunz classification	9.GA.05
Crystal system	Orthorhombic
Crystal class	Pyramidal (mm2) (same H-M symbol)
Space group	Fdd2
Unit cell	a = 18.4049(8) Å, b = 56.655(6) Å, c = 6.5443(4) Å; Z = 8
Identification
Color	Colorless, white, gray, yellowish brown
Crystal habit	As elongated prismatic crystals, commonly in hairlike tufts and aggregates of fibers; radiating compact masses; stalactitic; porcelaneous
Twinning	Characteristically twinned on {010} or {100}
Cleavage	Perfect on {110} and {110}
Fracture	Uneven
Tenacity	Brittle, masses tough
Mohs scale hardness	5
Luster	Vitreous, silky when fibrous
Streak	White
Diaphaneity	Transparent to translucent, opaque
Specific gravity	2.26
Optical properties	Biaxial (+)
Refractive index	nα = 1.505 nβ = 1.505 nγ = 1.505
Birefringence	δ = 0.001
2V angle	Measured: 80°
Other characteristics	May exhibit a small pyroelectric effect; piezoelectric
References	[2][3][4][5]

Mesolite is a tectosilicate mineral with formula Na₂Ca₂Si₉Al₆O₃₀·8H₂O. It is a member of the zeolite group and the natrolite subgroup,^[4] also resembling natrolite in appearance.

Mesolite crystallizes in the orthorhombic system and typically forms fibrous, acicular prismatic crystals or masses.^[3] Radiating sprays of needlelike crystals are not uncommon. It is vitreous in luster and clear to white in color. It has a Mohs hardness of 5 to 5.5 and a low specific gravity of 2.2 to 2.4. The refractive indices are nα=1.505 nβ=1.505 nγ=1.506.