Mineral Information and Data:

Epistilbite
Ca3(Si18Al6)O48 • 16H2O [CNMNC approved formula]

Named from the Greek epi - "near" and the mineral Stilbite. First Published 1826. Defined per nomenclature for zeolite minerals (IMA, 1997).

IMA status : Approved Species 1997 ()
CLASSIFICATION 
Dana
(8th edition) :
77.01.06.02  
  (77) Tectosilicate Zeolite group
  (77.01) true zeolites
  (77.01.06) Mordenite and related species
  
Nickel-Strunz
(10th edition) :
09.GD.45
  (09) Silicates
  (09.G) Tektosilicates with Zeolitic H2O
  (09.GD) Chains of 6-membered rings - tabular zeolites
  
Crystal system: Triclinic System
Point group (H-M): 1 — pedial
Space group: C2/m
Unit cell: a = 9.08Å, b = 17.74Å, c = 10.25Å β = 124.5° Z=3
Crystal Habit: Crystals prismatic, to 3 cm; in spherulitic or sheaf-like aggregates.
Twinning: Always on {100}, pseudo-orthorhombic; on {110} to form penetration crosses.
  
Color: Colorless, white, pinkish, yellowish; colorless in thin section.
Diaphaneity: Transparent to translucent
Luster: Vitreous
Hardness (Mohs): 4
Cleavage: {010}, perfect
Tenacity: Brittle
Fracture: Uneven
  
Polymorphism and Series: Dimorphous with goosecreekite
Geologic Setting: In cavities in basalts and gneisses.
Mineral Association: Zeolites, quartz
  
Other Properties: Piezoelectric. Gemstone Unlikely Available.

 

Epistilbite
Origin: Jalgaon, Maharashtra, India
Sample size: 6.5 x 4.5 x 3 cm
Photo: Rob Lavinsky

 

Epistilbite
(zoom-in of above)

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