Mineral Information and Data:

Ca4Fe2+2Al4[B2Si8O30](OH)2 [CNMNC approved formula]

Named from the Greek acine - "ax" in allusion to the acute shape of typical crystals and its Fe dominance. First published in 1911. Name changed from ferro-axinite (IMA, 2008)

IMA status : Renamed IMA Approved; 2008 ()
(8th edition) :  
  (56) Sorosilicate Si2O7 Groups and O, OH, F. and H2O
  (56.02) with cations in [4] and/or >[4] coordination
  (56.02.02) Axinite group
(10th edition) :
  (09) Silicates
  (09.B) Sorosilicates (dimer) structures
  (09.BD) Si2O7 groups, with additional anions; cations in tetrahedral [4] and greater coordination
Crystal system: Triclinic System
Point group (H-M): 1 — pinacoidal
Unit cell: a = 7.1437(4) Å, b = 9.1898(6) Å, c = 8.9529(4) Å α = 91.857(6)°, β = 98.188(5)°, γ = 77.349(4)°
Crystal Habit: Crystals typically flattened, axe-head-shaped, to 20 cm; granular, massive.
Color: Clove-brown, brown, plum-blue, pearl-gray; colorless to pale brown or blue in thin section
Diaphaneity: Transparent to translucent
Luster: Vitreous
Hardness (Mohs): 6.5 - 7
Measured Density: 3.25 - 3.28 g/cm3
Cleavage: Good on {100}, poor on {001}, {110}, and {011}
Tenacity: Brittle
Fracture: Uneven to conchoidal
Polymorphism and Series: Forms a series with axinite-(Mn).
Geologic Setting: In low- to high-grade regionally metamorphosed rocks, in contact metamorphosed rocks, and in pegmatites.
Mineral Association: Prehnite, andradite, hedenbergite, zoisite, actinolite, datolite, tourmaline, vesuvianite, calcite, albite, quartz
Synonyms/varieties: Ferro-axinite
Other Properties: Gemstone Readily Available.


Brown Axinite-(Fe) crystals with chlorite and adularia.
Origin: St. Gotthard, Switzerland
Sample size: 25 x 30 x 22 mm
Photo: Dan Weinrich


(zoom-in of above)