Charoite
| Charoite | |
|---|---|
| General | |
| Category | Silicate mineral |
| Formula | K(Ca,Na) 2Si 4O 10(OH,F)•H 2O |
| IMA symbol | Cha |
| 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 | 0.009 |
| Ultraviolet fluorescence | Weakly fluorescent |
| Common impurities | Al, Fe, Mn, Sr, Ba |
| Other characteristics | Radioactive 10.69% (K) |
| References | |
Charoite (/tʃæroʊ.aɪt/ CHAR-ow-ait) is a rare silicate mineral with the chemical composition K(Ca,Na)
2Si
4O
10(OH,F)•H
2O, first described in 1978. It is named after the Chara River, despite its being 70 kilometres (43 mi) away from the discovery place. When it was discovered, it was thought to be a fake, dyed purple to give it its striking appearance.