It is generally thought that quartz, the rock family that gives jewelers such gem staples as amethyst and black onyx, is the most common mineral on earth. Think again, some geologists say. That distinction rightfully belongs to feldspar, a rock group whose most famous gem member is moonstone.
But whether or not feldspar is the most common mineral found on earth, it just might be the most common mineral found around the home—at least in America. Feldspar, both in ground-up rock and clay form, is used in numerous home and beauty products. If, for example, you’ve got fire bricks in the den or Soft Scrub cleaning products in the kitchen, then you’ve got feldspar on the premises.
Miners in Oregon would like to see Oregon sunstone added to the long list of household feldspars. Two factors are working in the American gem’s favor to boost demand: quality and quantity. At their best, Oregon sunstones boast the traditional red and orange colors associated with this gem, as well as a wide variety of unique greens never before seen. Occasionally, pieces of rough are free enough of inclusions to permit faceting. Sunstone from India, the other major source of this gem, are invariably cut in cabochon form.
Oregon feldspar is known by two names, “sunstone” and “heliolite” (the latter a recent coinage based on the Greek word for sun, helios). Of the two names, “sunstone” is usually preferred by those familiar with both. How sunstone got its name is not known. Some think it originally referred to the gem’s similarity to the color of the setting sun. Others think the name stemmed from its reddish glints reminiscent of metal-flake paint.
Most likely it’s the latter, for sunstone is usually thought of as a phenomenon stone, thanks to the millions of copper platelets or hematite particles found in the Oregon and Indian varieties respectively. The spangled light reflections caused by these inclusions are variously and interchangeably described with play-of-color terms such as schiller (a German word, often used with moonstone, for a bluish or white sheen), “labradorescence” (vivid colorations in certain feldspar family members) and “iridescence” (intermingling of brilliant colors).
Curiously, none of these terms is correct for Oregon sunstone. Since the special effect for which this gem is known has more to do with light than color, the most accurate term, is the one least used: “aventurescence” (derived from the Italian word avventura, which means “by chance”).This is ironic since sunstone is classified by mineralogists as an aventurine feldspar. The word “aventurine,” like “aventurescence,” refers to the spangle phenomenon.
Realizing most collectors are still as unfamiliar with Oregon sunstone as we were, we inspected thousands of carats of goods for this article. Most were various shades of red and orange—from plum and raspberry to peach and salmon—while Indian stones tend to have golden or yellow body colors.