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
CategoryTectosilicate
Zeolite
Formula
(repeating unit)		Na2Ca2(Al2Si3O10)3·8H2O
IMA symbolMes[1]
Strunz classification9.GA.05
Crystal systemOrthorhombic
Crystal classPyramidal (mm2)
(same H-M symbol)
Space groupFdd2
Unit cella = 18.4049(8) Å,
b = 56.655(6) Å,
c = 6.5443(4) Å; Z = 8
Identification
ColorColorless, white, gray, yellowish brown
Crystal habitAs elongated prismatic crystals, commonly in hairlike tufts and aggregates of fibers; radiating compact masses; stalactitic; porcelaneous
TwinningCharacteristically twinned on {010} or {100}
CleavagePerfect on {110} and {110}
FractureUneven
TenacityBrittle, masses tough
Mohs scale hardness5
LusterVitreous, silky when fibrous
StreakWhite
DiaphaneityTransparent to translucent, opaque
Specific gravity2.26
Optical propertiesBiaxial (+)
Refractive indexnα = 1.505 nβ = 1.505 nγ = 1.505
Birefringenceδ = 0.001
2V angleMeasured: 80°
Other characteristicsMay exhibit a small pyroelectric effect; piezoelectric
References[2][3][4][5]

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.

Occurrence

It was first described in 1816 for an occurrence in the Cyclopean Islands near Catania, Sicily.[5] From the Greek mesos, "middle", as its composition lies between natrolite and scolecite.[4][5] Like other zeolites, mesolite occurs as void fillings in amygdaloidal basalt also in andesites and hydrothermal veins.[3]

Images
  • Mesolite
    Mesolite
  • "Puff ball" of mesolite in a basaltic vug
    "Puff ball" of mesolite in a basaltic vug
  • Mesolite often forms in fibrous crystals
    Mesolite often forms in fibrous crystals
  • A pocket of hairlike acicular crystals of mesolite growing off thomsonite
    A pocket of hairlike acicular crystals of mesolite growing off thomsonite
  • Fibrous crystal sample retrieved from caverns near Pune, India
    Fibrous crystal sample retrieved from caverns near Pune, India

References
  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. Mineralienatlas
  3. Handbook of Mineralogy
  4. Mindat.org
  5. Webmineral data


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