Axinite

Axinite
Axinite – Deposit Topotype, France
General
Category	Sorosilicates
Formula (repeating unit)	(Ca,Fe,Mn)3Al2BO3Si4O12OH or Ca2(Fe,Mn)Al2BSi4O15(OH)
Strunz classification	9.BD.20
Crystal system	Triclinic
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
Luster	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	[1][2]

Axinite is a brown to violet-brown, or reddish-brown bladed group of minerals composed of calcium aluminium boro-silicate, (Ca,Fe,Mn)₃Al₂BO₃Si₄O₁₂OH. 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^[3]
• Axinite-(Mg) or magnesioaxinite, Ca₂MgAl₂BOSi₄O₁₅(OH) magnesium rich, pale blue to pale violet; light brown to light pink^[4]
• Axinite-(Mn) or manganaxinite, Ca₂Mn²⁺Al₂BOSi₄O₁₅(OH) manganese rich, honey-yellow, clove-brown, brown to blue^[5]
• Tinzenite, (CaFe²⁺Mn²⁺)₃Al₂BOSi₄O₁₅(OH) iron – manganese intermediate, yellow, brownish yellow-green^[6]

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 x 3.5 x 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

• 

  faceted axinite, 1.02ct, Brazil

References

1. Axinite. Mineral Galleries
2. Axinite. Mindat
3. Handbook of Mineralogy: Ferroaxinite
4. Handbook of Mineralogy: Magnesioaxinite
5. Handbook of Mineralogy: Manganaxinite
6. Handbook of Mineralogy: Tinzenite