Bustamite

Bustamite
Bustamite (pink) with galena (grey) from Broken Hill, New South Wales, Australia. Specimen size 3.7 cm.
General
Category	Inosilicate
Formula (repeating unit)	CaMn2+Si2O6[1]
IMA symbol	Bst[2]
Strunz classification	9.DG.05 (10 ed) 8/F.18.40 (8 ed)
Dana classification	65.2.1.2
Crystal system	Triclinic
Crystal class	Pinacoidal 1 (same H-M symbol)
Space group	I1
Identification
Color	Light pink to brownish red Pink color fades on exposure to sunlight
Crystal habit	Usually tabular or equant to prismatic; commonly massive, often compact and fibrous
Twinning	Rare. Simple twins with (110) as the composition plane
Cleavage	{100} perfect; {110} and {110} good; {010} poor
Mohs scale hardness	5.5 to 6.5
Luster	Vitreous
Streak	White
Diaphaneity	Translucent to transparent
Specific gravity	3.32 to 3.43 (observed) 3.40 (calculated)
Optical properties	Biaxial (−), 2V=34° to 60°
Refractive index	nα = 1.640 – 1.695, nβ = 1.651 – 1.708, nγ = 1.653 – 1.710[3]
Birefringence	δ = 0.013 – 0.015 Dispersion r < v weak to strong
Pleochroism	Weak, X and Z orange, Y rose
Solubility	Partly soluble in HCl.[3]
Other characteristics	lattice: A B1 Specimens from the Franklin Mine are fluorescent red in longwave ultraviolet light.[4] Not radioactive
References	[5][6][7][8]

Bustamite is a calcium manganese inosilicate (chain silicate) and a member of the wollastonite group. Magnesium, zinc and iron are common impurities substituting for manganese. Bustamite is the high-temperature polymorph of CaMnSi₂O₆ and johannsenite is the low temperature polymorph. The inversion takes place at 830 °C (1,530 °F), but may be very slow.^[3]
Bustamite could be confused with light-colored rhodonite or pyroxmangite, but both these minerals are biaxial (+) whereas bustamite is biaxial (−).