Axinite

Chemical Composition: Ca₂(Fe, Mg, Mn)Al₂(BO₃/OH/Si₄O₁₂) (Complicated borate silicate)
Mohs' Hardness:6.5-7
Specific Gravity: 3.27-3.29
Cleavage: Perfect
Refractive Index: 1.675-1.685
Double Refraction: -0.010
Dispersion: None

Axanite was named by R. J. Hatly in 1799. He named it axanite for the crystals are shaped similarly to the head of an axe. The brownish-red crystals grow thin, with a sharp acute angle jutting out of the rock matrix. Axanite is triclinic, meaning it has no planes of symmetry or axes of rotation. In a similar fashion to apatite, axanite is actually four different minerals, which are often labeled the same. The minerals have the same crystalline structure but differ slightly in color, specific gravity and, of course, chemical composition.

The four different types of Axanite are:

• Ferro-axinite: contains iron ions, colored lilac brown to black, SG=3.31
• Magnesio-axinite: contains magnesium ions, colored pale blue to gray, SG=3.18
• Manganaxinite: contains manganese ions, colored yellow-orange, SG=3.32
• Tinzenite: contains both iron and manganese ions, colored yellow, SG=3.37

Axanite is usually found in compact msses, but it is not to be found in its crystalline form. It often forms on the walls of cavities in ancient silicate rocks. Notable occurances of axanite are in Le Bourg d'Osians in France, New Jersey, The Baja Peninsula, Brazil, Switzerland and Obira in Japan.

---

Sources:
Precious Stones, by Dr. Max Bauer. Charles E. Tuttle Company: Rutland Vermont and Tokyo, Japan, 1969
Gemstones of the World, by Walter Schumann. Sterling Publishing Co., New York, 1979
http://mineral.galleries.com/minerals/silicate/axinite/axinite.htm
http://27.1911encyclopedia.org/A/AX/AXINITE.htm

Ax"i*nite (?), n. [Named in allusion to the form of the crystals, fr. Gr. an ax.] Min.

A borosilicate of alumina, iron, and lime, commonly found in glassy, brown crystals with acute edges.

 

© Webster 1913.