Epistilbite

(n.)
A crystallized, transparent mineral of the Zeolite family. It is a hydrous silicate of alumina and lime.
  

General Information:
 Chemical Formula:
CaAl2Si6O16·5(H2O)
 Composition:
(Molecular Weight = 608.62 gm)
Calcium 6.59 % Ca
Aluminum 8.87 % Al
Silicon 27.69 % Si
Hydrogen 1.66 % H 
Oxygen 55.20 % O 
 Empirical Formula:
CaAl2Si6O16·5(H2O)
 Environment:
Alteration product in basalts.
 IMA Status:
Approved IMA 1972
 Locality:
Berufjord, Iceland.
 Name Origin:
From the Greek epi - "near" and the mineral Stilbite.
Physical Properties:
 Cleavage:
[010] Perfect
 Color:
white, yellowish white, reddish white, or brownish white.
 Density:
2.2 - 2.3, Average = 2.25
 Diaphaniety:
Transparent to translucent
 Habits:
Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline)., Spherical - Spherical, rounded aggregates., Twinning Common - Crystals are usually twinned.
 Hardness:
4-5 - Fluorite-Apatite
 Luminescence:
None.
 Luster:
Vitreous (Glassy)
 Streak:
white
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