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 [1][2][3][4]

Charoite (K(Ca,Na)2Si4O10(OH,F)·H2O)[4] is a rare silicate mineral, first described in 1978 and named for the Chara River.[3] It has been reported only from the Sakha Republic, Siberia, Russia.[4] It is found where a syenite of the Murunskii Massif has intruded into and altered limestone deposits producing a potassium feldspar metasomatite.[2][3]

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.[4]

References

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