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Chemical composition Complex borosilicate
Crystal system Triclinic
Habit Axe shaped.
Cleavage Perfect {100}
Fracture Uneven to conchoidal, brittle
Hardness 6.5 - 7
Optic nature Biaxial - (or +)
Refractive index 1.674 - 1.706
Birefringence 0.010 - 0.012
Dispersion Low, 0.018 - 0.020
Specific gravity 3.27-3.29
Lustre Bright vitreous
Pleochroism Moderate to Strong
A pinkish/greenish brown axinite.
Photo courtesy of Chaman Golecha, Gem Testing Laboratory, Jaipur.

Chemical composition

Ca3Al2BSi4O15(OH). Much variation in composition due to replacement of Ca by Fe, Mg, Mn. Therefore the composition may be written as (Ca, Mn, Fe, Mg)3Al2BSi4O15(OH)

  • +Mg - magnesioaxinite
  • If Fe more than Mn - Ferroaxinite
  • If Mn more than Fe - Manganaxinite
  • If Mn more than Fe and Ca less than 1.5 - tinzenite


Habit: broad and acute edged usually (axe shaped); varied habit; Also massive, lamellar, granular, curved. Generally in clusters, also tabular.



Clove Brown, rarely honey yellow or plum blue. Also pearly gray, greenish yellow; violet-brown; colorless-yellowish(Mn); pale violet/reddish (Mn), blue (Mg).


Transparent to semi transparent.


7-6.5 (directional)

Specific gravity

3.27-3.29 [Ferroaxinite:3.17-3.31; Magnesioaxinite:3.18; range 3.26-3.36]


Optic Character: anisotropic; Biaxial Negative (If high in Mg may turn +ve).
R.I.: nα = 1.674-1.693, nβ = 1.680-1.701 and nγ = 1.684-1.706.
Generally R.I.:1.67 to 1.68
Maximum birefringence: 0.010 - 0.012


Strong bands at 512, 494, 466 and sometimes 415nm; strong lines at 523, 444.


UV fluorescence: May show red-orange under SWUV


Strong depending on body colour and source. Generally olive green / violet blue and cinammon brown.


  • Andalusite: Lower S.G., spectrum, R.I. etc
  • Barite: Higher heft, lower hardness
  • Smoky Quartz: Lower Heft (floats 2.88), bulls eye optic figure, R.I. etc
  • Sphene: Doubling, dispersion, spectrum


Geological occurrence:
Occurs in cavities of granite or diabase; contact zones

Geographical locations:
Good crystals from St. Cristophe, France; various american localities; Bahia, Brazil; Cornwall, England; Mexico; Also in California; Sri Lanka; Nevada (masses); New Jersey; Germany; Norway; Finland; USSR; Japan; Tasmania; Switzerland (Tinzenite); Tanzania (Magnesoaxinite); Sri Lanka (ferro axinite-cinnamon brown)