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Category Tectosilicate
(repeating unit)
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
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 [1][2][3][4]

Mesolite is a tectosilicate mineral with formula Na2Ca2(Al2Si3O10)3·8H2O. It is a member of the zeolite group and is closely related to natrolite which it also resembles in appearance.

Mesolite crystallizes in the orthorhombic system and typically forms fibrous, acicular prismatic crystals or masses.[2] 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.


It was first described in 1816 for an occurrence in the Cyclopean Islands near Catania, Sicily.[4] From the Greek mesos, "middle", as its composition lies between natrolite and scolecite.[3][4] Like other zeolites, mesolite occurs as void fillings in amygdaloidal basalt also in andesites and hydrothermal veins.[2]