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Epistilbite
Current inventory:  0 gems
 

Chemistry:  CaAl₂Si₆O₁₆ ·5(H₂O)
[Hydrated Calcium Aluminum Silicate]

Discovered in 1826;   IMA status: Valid (pre-IMA; Grandfathered).
Epistilbite is named from the Greek word, epi for near, and stilbite for its similarity to the mineral.

Classification

Mineral Classification:

Silicates

Strunz 8th Ed. ID:

8/J.22-40

Nickel-Strunz 10th Ed. ID:

9.GD.45

9 : SILICATES (Germanates)
G : Tektosilicates with zeolitic H₂O; zeolite family
D : Chains of 6-membered rings – tabular zeolites

Related to:

Zeolite Group. Ferrierite - Laumontite Series. Dimorph of Goosecreekite.

Crystal Data

Crystallography:

Triclinic - Pinacoidal

Crystal Habit:

Crystals prismatic, to 3 cm; in spherulitic or sheaflike aggregates.

Twinning:

Always on [100], pseudo-orthorhombic; on [110] to form penetration crosses.

Physical Properties

Cleavage:

[010] Perfect

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Hardness (Mohs):

4.0 - 5.0

Density:

2.20 - 2.30 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Other:

Piezoelectric

Optical Properties

Color:

Colorless, White, Yellowish, Pinkish, Brownish White

Transparency:

Transparent to Translucent

Luster:

Vitreous

Refractive Index:

1.485 - 1.519  Biaxial ( - )

Birefringence:

0.0100

Dispersion:

Relatively Strong; r < v

Pleochroism:

None

Occurances

Geological Setting:

In cavities in basalts and gneisses.

Common Associations:

Quartz, Zeolites

Common Impurities:

Fe, Mg, Na, K

Co-Type Localities:

Teigarhorn, Berufjördur, Suður-Múlasýsla, Iceland
Breiðdalur- Berufjörður area, Suður-Múlasýsla, Iceland

Year Discovered:

1826

View mineral photos:

Epistilbite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Epistilbite is a very rare member of the Zeolite Group of minerals that includes over 40 minerals and these gem-type minerals: Analcime, Barrerite, Chabazite, Epistilbite, Gmelinite-Na, Goosecreekite, Mordenite, Natrolite, Pollucite, Scolecite, Stellerite, Stilbite, Thomsonite and Yugawaralite. Epistilbite often forms in the petrified bubbles, called vesicles, of slightly metamorphosed volcanic rocks and also in some pegmatites.

Although Epistilbite is relatively rare, many localities are known. Exceptional crystals from around the Berufjord, Iceland. Found near San Piero in Campo, Elba, Italy. At Giebelsbach, near Fiesch, Valais, Switzerland. In Japan, at Kuroiwa, Niigata Prefecture; Yugawara, Kanagawa Prefecture; and elsewhere. Large crystals from Nasik and Khandivali quarry, Bombay, Maharashtra, India. In the USA, large crystals from Kosmos, near Morton, Lewis County, Washington; at Goble, Columbia County, Oregon.
 

  
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