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Axinite

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Axinite
Manganaxinite
General
CategoryCyclosilicates
Formula
(repeating unit)
(Ca,Fe,Mn)3Al2BO3Si4O12OH or Ca2(Fe,Mn)Al2BSi4O15(OH)
IMA symbolAx[1]
Strunz classification9.BD.20
Crystal systemTriclinic
Crystal classPinacoidal (1)
(same H-M symbol)
Space groupP1
Identification
ColorReddish brown to yellow to colorless. Blue, violet, grey.
Crystal habitTabular, wedge shaped crystals
CleavageGood on {100}
FractureConchoidal
Mohs scale hardness6.0–7.5
LusterVitreous
StreakWhite
Specific gravity3.18–3.37
Optical propertiesBiaxial (−)
Refractive indexnα = 1.672–1.693
nβ = 1.677–1.701
nγ = 1.681–1.704
Birefringenceδ = 0.011
PleochroismStrong
References[2][3]

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[4]
  • Axinite-(Mg) or magnesioaxinite, Ca2MgAl2BOSi4O15(OH) magnesium rich, pale blue to pale violet; light brown to light pink[5]
  • Axinite-(Mn) or manganaxinite, Ca2Mn2+Al2BOSi4O15(OH) manganese rich, honey-yellow, clove-brown, brown to blue[6]
  • Tinzenite (CaFe2+Mn2+)3Al2BOSi4O15(OH) iron – manganese intermediate, yellow, brownish yellow-green[7]

Axinite is sometimes used as a gemstone.[8]

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References

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  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Axinite Archived November 19, 2008, at the Wayback Machine. Mineral Galleries
  3. ^ Axinite. Mindat
  4. ^ Handbook of Mineralogy: Ferroaxinite
  5. ^ Handbook of Mineralogy: Magnesioaxinite
  6. ^ Handbook of Mineralogy: Manganaxinite
  7. ^ Handbook of Mineralogy: Tinzenite
  8. ^ Tables of Gemstone Identification By Roger Dedeyne, Ivo Quintens p.147