Axinite is a group of brown to violet-brown or reddish brown minerals that sometimes occur in gem quality. Axinite is distinctive due to its strong vitreous luster when polished and its interesting pyro- and piezo-electric properties. Axinite is popular with mineral collectors because of its unusual crystal structure.
Axinite is referred to as a "group" because there are a number of minerals with a slightly different chemical composition, but with a common crystal structure. All the axinite minerals have a triclinic structure with unique, flattened spatula-shaped crystals.
The different members of the axinite group vary slightly in composition. The axinites are defined as calcium aluminum boro-silicates by composition. Members of the group are distinguished depending on whether the calcium is replaced by iron, magnesium or manganese. As the chemical composition varies, there are corresponding differences in color and specific gravity or density.
The most common axinite varieties are:
» Ferro-axinite; iron rich, lilac-brown to black with a specific gravity of 3.31.
» Magnesio-axinite; magnesium rich, pale blue to gray with a specific gravity of 3.18.
» Manganaxinite; manganese rich, yellow-orange with a specific gravity of 3.32.
» Tinzenite; iron & manganese intermediate, yellow, specific gravity of 3.37.
Axinite has a hardness of 6.5 to 7 on the Mohs scale and a refractive index of 1.656 to 1.704. It is a strongly pleochroic gem, meaning it displays different colors when viewed from different angles.
Axinite is a fairly rare gem. Though it is sufficiently hard to be used for jewelry, it is so uncommon that few jewelers work with it. Axinite deposits are found in Brazil, France, Mexico (especially Baja California), Russia, Sri Lanka, Tanzania and Pakistan.
- First Published: October-13-2009
- Last Updated: August-16-2017
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