Axinite

(Ca,Fe,Mn)₃Al₂BO₃Si₄O₁₂OH or Ca₂(Fe,Mn)Al₂BSi₄O₁₅(OH)IMA symbolAx^[1]Strunz classification9.BD.20Crystal systemTriclinicCrystal classPinacoidal (1)
(same H-M symbol)Space groupP1IdentificationColorReddish brown to yellow to colorless. Blue, violet, grey.Crystal habitTabular, wedge shaped crystalsCleavageGood on {100}FractureConchoidalMohs scale hardness6.0–7.5LusterVitreousStreakWhiteSpecific gravity3.18–3.37Optical propertiesBiaxial (−)Refractive indexn_α = 1.672–1.693
n_β = 1.677–1.701
n_γ = 1.681–1.704Birefringenceδ = 0.011PleochroismStrongReferences^[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]

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

References

BoratesCarbonatesOxides

Simple	Hausmannite Manganite Manganosite Nsutite Pyrolusite
Mixed	Birnessite Bixbyite Ferrocolumbite Ferrotantalite Galaxite Jacobsite Manganotantalite Psilomelane (calvonigrite) Romanèchite Tantalite Todorokite Umber

PhosphatesSilicatesSulfidesOther