Although sunstone and moonstone are both members of the feldspar group, the resemblance stops there. While cool moonstone’s phenomenal varieties offer a soft and gentle adularescent glow, warm sunstone’s phenomenal varieties show a distinct and lively glitter called aventurescence.
Aventurescence is a sparkly, metallic-looking luster caused by flat, reflective inclusions. Although most sunstones have yellow, orange, or brown body-color, not all sunstone is aventurescent. The appearance of the phenomenon depends upon the size of the inclusions. Small inclusions create a reddish or golden sheen on top of any bodycolor. Larger inclusions create attractive, glittery reflections. Sunstone inclusions can be hematite, copper, or some other mineral.
Not all feldspars that bear the name “sunstone” are from the same side of the feldspar family—both the orthoclase and the plagioclase species boast a sunstone variety of feldspar.
“Orthoclase sunstone” belongs to the monoclinic crystal system. While Oligoclase sunstone is plagioclase feldspar that belongs to the triclinic crystal system.
The name sunstone refers to the gem’s appearance rather than to its chemical makeup. There are many sunstone varieties. If aventurescence is present, gemologists call it aventurine feldspar. The aventurine feldspar from India has a red-brown body-color and sunny glitter. It’s perhaps the best-known sunstone variety.
A mine in the US state of Oregon produces a number of sunstone varieties. The increased supply from this mine has made sunstone more available to the general public. Because many of the sunstone types are unique to the rugged high-desert area in South Central Oregon, they’re being marketed as “all-American” gemstones.
Oregon sunstone is a transparent feldspar with copper inclusions. It comes in a colorless form, as well as in a wide variety of colors for instance pale yellow, pink with brilliant aventurescence, orange, red, green, and blue-green.
The transparent yellow, green, and red varieties are plagioclases from Oregon’s Plush and Ponderosa mines.The vivid red version is often marketed as “spinel red,” and its vivid hue—if not its hardness—this could rivals spinel or even ruby.
All Oregon sunstones have an extra sheen that’s caused by copper inclusions, even if the inclusions aren’t large enough to create actual aventurescence. Some Oregon sunstones are either bicolored or tricolored, like some tourmalines. Rarely, you may find Oregon sunstones display color change effect.
Currently, the top deep green, deep red, and intense bicolored sunstones are considered extra fine.
Oregon sunstone isn’t treated, making it all-natural as well as all-American. These are selling points that US sunstone producers emphasize in their attempt to bring the gem to a wider audience.
In 2004, sunstones from 3 to 5 cts. wholesaled for $10 to $30 per carat in commercial quality, and for $350 to $1,000 in extra-fine quality.
Oregon Sunstones are comprised of the mineral feldspar and were formed through volcanic action. Feldspar crystals are found in several locations throughout the globe. The pink schiller, red, bi-colored and green varieties are currently found only in Oregon.
Of the colored varieties, pink schiller is the most common. Red is next in rarity. Green and multi-colored stones are very rare. Exceptionally rare is a blue-green variety. These are rare and beautiful stones.
The Oregon Sunstone was made the official Oregon State Gemstone in 1987. With a hardness of 6.2-7.5 on the mohs scale. Oregon Sunstone Jewelery and Sunstone gemstones are an excellent investment. Oregon Sunstones are often referred to as the "Oregon Diamond".
Oregon sunstone is expensive to mine—a ton of rock typically contains only one pound (0.45 kilogram) of sunstone. And only a fraction is gem quality.
Sunstone’s scarcity and the unpredictable availability of its different color varieties make it challenging to market.
Tanzania has been hosting many important gem over the past decades for instance, tanzanite, charysoberyl, spinel, tsavorite, ruby, and sapphire.The most recent aventurescent feldspar to make a splash in the market, is that from Tanzania, which has combination of both hematite and/or copper inclusions. Both transparent and translucent pieces are available and in the best specimens the phenomenon is multi-colored.
CUTTING AND POLISHING OF SUNSTONE
Oregon Sunstone is a genuine pleasure to work with. At a hardness of 6.5 to 7.2, Dust Devil Oregon Sunstone cuts and polishes quickly and easily, yet is suitable for any jewelry application.
Although sunstone has a critical angle of 41 degrees, and some references recommend culet angles of 43 and up, in our experience a culet angle of 45 degrees gives the best performance.
ORIENTATION OF CLEAVAGE:
Cleavage seldom gives any trouble in sunstone. Most often, it is best to orient stones according to color and schilller first, then according to yield, leaving cleavage as the last concern. In a given stone, if cleavage is to be considered, orient the cleavage plane seven to ten degrees away from the table.
Note that on occasion faces that fall close to the cleavage plane may feel softer, cutting somewhat faster than their neighbors. If you experience this, use a light touch and be prepared to consider the tips on polishing given below.
ORIENTATION FOR COLOR
Color in sunstone usually occurs in a bulls-eye pattern - a spot of color surrounded by a clear or light straw-colored rind. The best color performance for faceted stones is achieved by focusing the available color at the culet of the stone and placing as much color as possible in the pavilion:
Such orientation will cause light that enters the crown to reflect through the color zone before exiting the stone. This stone was cut with such orientation:
Alternately, if the size and placement of the color zone permits, orient it beneath and parallel to the table:
ORIENTATION OF SCHILLER
In evaluating rough for schiller, it must be remembered that faceted stones sparkle by transmitting light while schiller sparkles by reflecting light. Once a light ray is reflected by a plate of schiller it will no longer be available for the stone to refract and transmit. Also, lit from behind, schiller can only cast a shadow.
In this photo, streaks of schiller appear as copper-colored shadows. Because they are lit from behind, the schiller can only cast a shadow toward the viewer:
Although sunstone is not a mainstream gem, the warm and sparkling stone can attract followers of innovative jewelry design. The late 1990s saw an increase in the selection of sunstone by award-winning designers. An outstanding 13-ct. gem carving made of red-orange Oregon sunstone won third place in the combination division of the American Gem Trade Association’s Cutting Edge Awards for 1997. The current sunstone market is a specialized one, consisting of upscale jewelry designers, collectors, gem carvers, and tourists to the Oregon desert seeking a precious all-American souvenir.
GOLDSTONE-An imitation of aventurine feldspar made of glass that contains small copper crystals