Oregon Sunstones
Oregon sunstone, the official state gemstone since 1987, is natural copper-bearing labradorite feldspar. Some examples exhibit red to green dichroism, and exceptional cut gemstones larger than 5 ct can sell for more than $1,000 per carat depending on color, clarity and cut.
Oregon sunstone, also known as heliolite, is a plagioclase feldspar with a range of colors from water clear, yellow, soft pink or salmon, light red to blood red, green and extremely rare teal / blue. The color appears to vary systematically with small amounts of copper and may depend on both the amount and the size of individual copper particles present in the stone.
Pale yellow stones have a copper content as low as 20 parts per million (ppm) (0.002 percent), green stones contain about 100 ppm per million (0.01 percent), and red stones have up to 200 ppm (0.02 percent) copper. Some of the deeper colored stones have bands of varying color, and a few stones are dichroic, that is, they show two different colors when viewed from different directions.
Many stones appear to be perfectly transparent at first, but when they are viewed in just the right direction, a pink to red metallic shimmer flashes from within the stone. This effect is called "schiller" or "aventurescence" and is caused by light reflecting from minute parallel metallic platelets suspended in the sunstone. When viewed along their edges, the platelets are invisible to the naked eye; when viewed, however, perpendicular to their surfaces, they reflect light simultaneously from each platelet, creating a mirror effect.
