Gyrolite

Gyrolite
240px Gyrolite
General
Category	Phyllosilicate
Formula (repeating unit)	NaCa16Si23AlO6(OH)8·14H2O
Strunz classification	09.EE.30
Dana classification	73.2.2c.1
Crystal symmetry	Triclinic space group: P1
Unit cell	a = 9.74 Å, b = 9.74 Å, c = 22.4 Å; α = 95.71°, β = 91.51°, γ = 120.01°; Z=4
Identification
Color	White, colorless, green, yellow or brown
Crystal habit	Compact, lamellar, platy
Crystal system	Triclinic
Twinning	Lamellar
Cleavage	Perfect on {001}
Tenacity	Brittle
Mohs scale hardness	2½
Luster	Vitreous, pearly
Diaphaneity	Transparent, translucent, opaque
Density	2.45 - 2.51
Optical properties	Biaxial (-)
Refractive index	nα = 1.535 nβ = 1.548 nγ = 1.549
Birefringence	δ = 0.0140
References

Gyrolite (NaCa₁₆Si₂₃AlO₆(OH)₈·14H₂O) is a silicate mineral that is usually associated with zeolites. It most commonly is found as spherical or radial formations in hydrothermally altered basalt and basaltic tuffs. These formations can be glassy, dull or fibrous in appearance.

Gyrolite is also known as Centrallasite, Glimmer Zeolite or Gurolite.

Discovery and occurrence

It was first described in 1851 for an occurrence at The Storr on the isle of Skye, Scotland and is named from the Greek word for circle, guros, based on the round form in which it is commonly found.

Minerals associated with gyrolite include apophyllite, okenite and many of the mother zeolites. Gyrolite is found in Scotland, Ireland; Italy, Faroe Islands, Greenland, India, Japan, USA, Canada and various other localities.