Mesolite
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 | |
|---|---|
 Mesolite from Bombay collected in the 18th century by Dr John Hunter | |
| General | |
| Category | Tectosilicate Zeolite |
| Formula (repeating unit) | Na2Ca2(Al2Si3O10)3·8H2O |
| 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 | [1][2][3][4] |
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.
Occurrence
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]
Images
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Mesolite
"Puff ball" of mesolite in a basaltic vug
Mesolite often forms in fibrous crystals
A pocket of hairlike acicular crystals of mesolite growing off thomsonite
Fibrous crystal sample retrieved from caverns near Pune, India