Thursday, 12 December 2013

Oregon Sunstone

Sunstone is a plagioclase feldspar, which when viewed from certain directions exhibits a brilliant spangled appearance; this has led to its use as a gemstone. It has been found in Southern Norway, and in some United States localities. It is the official gemstone of Oregon.

Oregon sunstone is found in Harney County, Oregon and in eastern Lake County north of Plush. Oregon sunstone contains inclusions of copper crystals. The copper leads to variant color within some stones, where turning one stone will result in manifold hues: the more copper within the stone, the darker the complexion.
Feldspars are silicate minerals that contain variable amounts of sodium (Na), potassium (K), and calcium (Ca). Labradorite belongs to the plagioclase feldspar series, which forms a solid solution between anorthite (CaAl2Si2O8) and albite (NaAlSi3O8). Oregon sunstone, which contains substantially more calcium than sodium, has a composition of about 70% anorthite and 30% albite.
Controversy surrounding treated copper-bearing feldspar has hurt Oregon Sunstone mining. In the early 2000s, Asian treaters perfected a method of diffusing copper into pale feldspar, flooding the market with low-priced, attractive red and green gems—which destabilized the market for Oregon sunstone. Promoted as “andesine” and purportedly from mines in Congo or Tibet, this material was subsequently found to be treated, but the resulting furor hindered the public’s trust in natural copper-bearing feldspar. Despite this setback, Oregon sunstone miners have strived to rebuild the market, and there are signs of renewed consumer interest in their one-of-kind gems.