Tinaksite

Tinaksite (chemical formula K₂Na(Ca,Mn²⁺)₂TiO[Si₇O₁₈(OH)])^[3] is a mineral found in northern Russia. Tinaksite can be grayish-white, yellowish, orange, or brown,^[2] and it is often found in charoite.^[5] Its name is derived from its composition: titanium (Ti), sodium (Na) potassium (K) and silicon (Si). The International Mineralogical Association first recognized tinaksite as a mineral in 1965.

Tinaksite
Tinaksite (brown) and associated charoite (lilac).
General
Category	Silicate mineral
Formula	K2Na(Ca,Mn2+)2TiO[Si7O18(OH)]
IMA symbol	Tnk[1]
Strunz classification	9.DG.75
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
Space group	P1
Identification
Color	Pink, pale yellow, light brown
Crystal habit	Fibrous, crystalline or prismatic, crystalline, or radial, crystalline
Cleavage	Perfect in one direction, indistinct in one direction
Mohs scale hardness	6
Luster	Vitreous to glassy
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	2.82
Optical properties	Biaxial (+)
Refractive index	nα = 1.593 nβ = 1.621 nγ = 1.666
Birefringence	δ = 0.073
References	[2][3][4]