Stilbite

General

 

Category: Tectosilicate, Zeolite

 

Formula: (repeating unit) Stilbite-Ca: NaCa4(Si27Al9)O72·28(H2O)

Stilbite-Na: Na9(Si27Al9)O72·28(H2O)

 

Strunz classification: 8/J.23-30 or 9.GE.10

 

Dana classification: 77.1.4.3

 

Identification

 

Formula mass: Stilbite-Ca: 2,840 gm Stilbite-Na: 2,864 gm

 

Color: Usually colorless, white or pink

 

Crystal habit: Thin tabular, aggregates sheaf-like or in bow-ties, also fibrous and globular

 

Twinning: Very common on {001}

 

Cleavage: Perfect on {010}

 

Fracture: Conchoidal or uneven

 

Tenacity: Brittle

 

Mohs scale hardness: 3.5 to 4

 

Luster: Vitreous, pearly on {010}

 

Streak: White

 

Diaphaneity: Transparent to translucent

 

Specific gravity: 2.12 to 2.22

 

Optical properties: Biaxial (-)

 

Refractive index: Nx = 1.479 to 1.492, Ny = 1.485 to 1.500, Nz = 1.489 to 1.505

 

Fusibility: Easily fused by blowpipe (~1050 °C) to produce a white "enamel"

 

Solubility: Decomposes in HCl

Done