Chemistry:Axinite

Axinite
Manganaxinite
General
Category	Cyclosilicates
Formula (repeating unit)	(Ca,Fe,Mn) 3Al 2BO 3Si 4O 12OH or Ca 2(Fe,Mn)Al 2BSi 4O 15(OH)
Strunz classification	9.BD.20
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
Space group	P1
Identification
Color	Reddish brown to yellow to colorless. Blue, violet, grey.
Crystal habit	Tabular, wedge shaped crystals
Cleavage	Good on {100}
Fracture	Conchoidal
Mohs scale hardness	6.0–7.5
|re|er}}	Vitreous
Streak	White
Specific gravity	3.18–3.37
Optical properties	Biaxial (−)
Refractive index	nα = 1.672–1.693 nβ = 1.677–1.701 nγ = 1.681–1.704
Birefringence	δ = 0.011
Pleochroism	Strong
References

Axinite is a brown to violet-brown, or reddish-brown bladed group of minerals composed of calcium aluminium boro-silicate, (Ca,Fe,Mn)
3Al
2BO
3Si
4O
12OH. Axinite is pyroelectric and piezoelectric.

The axinite group includes:

• Axinite-(Fe) or ferroaxinite, Ca₂Fe²⁺Al₂BOSi₄O₁₅(OH) iron rich, clove-brown, brown, plum-blue, pearl-gray
• Axinite-(Mg) or magnesioaxinite, Ca₂MgAl₂BOSi₄O₁₅(OH) magnesium rich, pale blue to pale violet; light brown to light pink
• Axinite-(Mn) or manganaxinite, Ca₂Mn²⁺Al₂BOSi₄O₁₅(OH) manganese rich, honey-yellow, clove-brown, brown to blue
• Tinzenite (CaFe²⁺Mn²⁺)₃Al₂BOSi₄O₁₅(OH) iron – manganese intermediate, yellow, brownish yellow-green

Axinite is sometimes used as a gemstone.

Gallery

• 

  Clove-brown axinite crystals to 2.3 cm set atop matrix from the West Bor Pit at Dalnegorsk, Russia

• 

  Chloritized bladed crystals of axinite forming on adularia from the Swiss Alps

• 

  Tinzenite on calcite, 4.5 × 3.5 × 3 cm. Wessels Mine, Kalahari manganese fields, Northern Cape Province, South Africa

• 

  Manganaxinite (Axinite-(Mn)), with sharp curving crystals to 4 cm. West Bor Pit at Dalnegorsk, Russia