Charoite

Charoite
General
Category	Silicate mineral
Formula (repeating unit)	K(Ca,Na)2Si4O10(OH,F)·H2O
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/m
Identification
Color	Violet, lilac, light brown
Crystal habit	Fibrous, massive
Cleavage	Good in three directions
Fracture	Conchoidal
Mohs scale hardness	5 - 6
Luster	Vitreous to pearly
Streak	White
Diaphaneity	Translucent
Specific gravity	2.54 - 2.58
Optical properties	Biaxial (+)
Refractive index	nα = 1.550 nβ = 1.553 nγ = 1.559
Birefringence	δ = 0.009
Other characteristics	Weakly fluorescent
References

Charoite (K(Ca,Na)₂Si₄O₁₀(OH,F)·H₂O) is a rare silicate mineral, first described in 1978 and named for the Chara River. It has been reported only from the Sakha Republic, Siberia, Russia. It is found where a syenite of the Murunskii Massif has intruded into and altered limestone deposits producing a potassium feldspar metasomatite.

Charoite is translucent lavender to purple in color with a pearly luster. Charoite is strictly massive in nature, and fractures are conchoidal. It has an unusual swirling, fibrous appearance, sometimes chatoyant, and that, along with its intense color, can lead many to believe at first that it is synthetic or enhanced artificially.

Though reportedly discovered in the 1940s, it was not known to most of the world until its description in 1978. It is said to be opaque and unattractive when found in the field; a fact that may have contributed to its late recognition.

Charoite occurs in association with tinaksite and canasite.

Gallery

• 
  Charoitite, a charoite-dominated potassic metasomatite rock from the type area. Photo is 5.7 cm wide.
• 
  Charoite postage stamp, 2000, from a series commemorating "300 Years of Mining and Geological Service in Russia."