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. Like other zeolites, mesolite occurs as void fillings in amygdaloidal basalt.Mesolite crystallizes in the monoclinic system and typically forms fibrous, acicular prismatic crystals or masses. Radiating sprays of needle like 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.
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(n.)
A zeolitic mineral, grayish white or yellowish, occuring in delicate groups of crystals, also fibrous massive. It is a hydrous silicate of alumina, lime, and soda.
  

General Information:
 Chemical Formula:
Na2Ca2Al6Si9O30·8(H2O)
 Composition:
(Molecular Weight = 1,164.90 gm)
Sodium 3.95 % Na
Calcium 6.88 % Ca
Aluminum 13.90 % Al
Silicon 21.70 % Si
Hydrogen 1.38 % H 
Oxygen 52.19 % O 
 Empirical Formula:
Na2Ca2Al6Si9O30·8(H2O)
 Environment:
Occurs in amygdaloidal basalt and similer rocks.
 IMA Status:
Approved IMA
 Locality:
Cyclopean Islands northeast of Catania, Sicily.
 Name Origin:
From the Greek mesos - "middle."
Physical Properties:
 Cleavage:
[101] Perfect, [001] Perfect
 Color:
white, gray, or pale yellow.
 Density:
2.2 - 2.4, Average = 2.29
 Diaphaniety:
Transparent to translucent
 Habits:
Acicular - Occurs as needle-like crystals., Capillary - Very slender and long, like a thread or hair (e.g. millerite)., Spherical - Spherical, rounded aggregates.
 Hardness:
5 - Apatite
 Luminescence:
None.
 Luster:
Vitreous - Silky
 Streak:
white
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