Axinite

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Axinite
Axinite-Oisan.jpg
Axinite – Deposit Topotype, France
General
Category Sorosilicates
Formula
(repeating unit)
(Ca,Fe,Mn)3Al2BO3Si4O12OH or Ca2(Fe,Mn)Al2BSi4O15(OH)
Strunz classification 09.BD.20
Identification
Color Reddish brown to yellow to colorless. Blue, violet, grey.
Crystal habit Tabular, wedge shaped crystals
Crystal system Triclinic
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]

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