Axinite is a group of brown to violet-brown or reddish brown minerals that sometimes occur in gem quality. Axinite is distinctive for its strong vitreous luster when polished, and its interesting pyro- and piezo-electric properties. Axinite is also popular with mineral collectors due to its unusual crystal structure.
Axinite is referred to as a "group" because there are a number of minerals with 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. But the different members of the group are distinguished depending on whether they 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:
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: October-13-2009
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