Chiolite

Chiolite is a tetragonal-ditetragonal dipyramidal mineral, composed of sodium, fluorine, and aluminium. The name originates from the combination of the Greek words for snow (χιώυ) and stone (λίθος). It is an allusion to its similarity and appearance to cryolite (ice stone).[2] It was first discovered in the Ilmen mountains, Russia, in 1846, but otherwise can be found in Greenland and Virginia. It occurs in some granite pegmatites.[3] It has been a valid species from the same year of its discovery. It consists of 24.89% sodium, 17.53% aluminium, 57.59% fluorine.[4]

Chiolite
General
Category	Mineral
Formula (repeating unit)	Na5Al3F14
IMA symbol	Cio[1]
Strunz classification	03.CE.05
Dana classification	11.06.11.01
Crystal system	Tetragonal
Crystal class	4/mmm (4/m 2/m 2/m) - Ditetragonal Dipyramidal
Space group	P4/mnc
Unit cell	511.06 ų
Identification
Color	Nearly colorless, snow white
Twinning	On {011}
Cleavage	Perfect on {001}, distinct on {011}
Mohs scale hardness	3.5 - 4
Luster	Vitreous, pearly, greasy
Streak	White
Diaphaneity	Transparent, translucent
Specific gravity	2.998
Density	2.998 measured, 2.989 calculated
Optical properties	Uniaxial (-)
Refractive index	nω = 1.349 nε = 1.342
Birefringence	0.007