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NATURAL SELECTION

 

 

SUNSTONE MARKETS AND OVERVIEW

                   © Joel E. Arem, PhD, FGA rev. 7-02

The market for sunstone has been growing for nearly 50 years. Tiffany & Co. at one time had even considered using the gem in a major marketing program! The material is mined chiefly in the state of Oregon; it is the Oregon State Gemstone, and is the largest contributor to the state’s gemstone production revenues. However the mining is primarily in the hands of small operations, ranging from weekend diggers to 5 to 6-person crews with limited machinery and very small operating budgets.

Oregon sunstone occurs in lava flows and, because of the presence of copper in the rock, comes out in a wide variety of colors: very pale yellowish-brown, green, blue-green, blue, orange, and red. Copper inclusions also create a metallic sheen within some of the material. This effect is known as "Schiller" and makes the gems more or less opaque, but also creates a unique and attractive appearance, sometimes with a pinkish tone. These gems are suitable mainly for cabochons. The color in Oregon sunstone is thus extremely variable, and usually there are several colors present in an individual crystal. The same crystal would therefore produce a huge variety of apparent colors if cut in different orientations. Moreover the attractive coloration generally is concentrated in small areas within a near-colorless matrix, limiting severely the available options for cutting an attractive gemstone and also drastically reducing the potential the yield of cut gems from the rough.

The huge variation in color and optical effects, pronounced zoning, abundant flaws and inclusions, general small size of rough and variability in selection of orientation all results in a significant market factor: it is extremely difficult to produce large numbers of cut gems that look exactly the same. This is a major disadvantage in a marketplace that demands uniformity in order to support the mass-production and distribution of jewelry. In order to produce a large number of gems of (visually) indentical size and appearance it is therefore necessary to cut a truly immense number of stones from which to select and match. The cost of cutting such a large number of gems has heretofore far exceeded the cash resources of any of the existing sunstone mining operations.

The result of this limitation is that, despite abundant market awareness and publicity and a growing base of demand, there has never been large-scale availability of sunstone. As a result there has never been sufficient interest among major gem and jewelry distributors to publicize and promote sunstone and bring the material into prominence in the world market. Sunstone is a feldspar, and all feldspars have a hardness of approx. 6 on the Mohs scale. By comparison, tanzanite is about 6.5, opal is 5.5, garnets and zircon are 6+ but very brittle, and most gems used in rings are 7+. Sunstone is very durable and wears very well in jewelry, actually probably better than opal, tanzanite, garnet and zircon. The major sunstone producers have now created a "Co-op" for mutual assistance in mining, cutting and promotion. Their commitment is to try to bring sunstone fully onto the world gemstone "stage" through the promotion of material from many localities. However, the basic problems of poor infrastructure, small deposits, limited capital for both mining and cutting, and extreme variation in appearance among cut gems, all affect Oregon sunstone production and marketing.

There is, however, a unique sunstone deposit that is in North America but some considerable distance from the established Oregon claims. The lava flow in this deposit is a very "pure" basalt and contains no measurable copper; the only significant metallic component is iron, which is the 4th most abundant element in the earth’s crust and present in virtually all igneous rocks. The feldspar in this flow apparently crystallized at depth for a very long time before the rock was extruded to the earth’s surface, and grew with no chemical contamination from impurities that would impede crystal growth and perfection. As a result, the feldspar crystals are a bright, pure golden yellow color (due to ferric iron) with no apparent color variation at all.

The crystals also occur in sizes up to as much as 150 grams (typical Oregon size is 5-15 grams) and nearly all the crystals are glassy and transparent and almost completely devoid of imperfections. There are no optical effects (Schiller) to reduce transparency, and no color zoning whatever. The crystals can therefore be cut without regard to orientation and extremely high yields are routinely achieved (30-50%, versus the 5-10% from Oregon rough). The average sized crystals in this flow would yield cut gems between 3 and 10 carats (the Oregon average would be 1-3 carats). The largest cut gem recorded from Oregon rough (a stone labeled "the Promise" that also displays prominent Schiller under the table) is about 54 carats. By contrast, this deposit has already produced a nearly-flawless cut stone of 258 carats (the world’s largest plagioclase feldspar gem, by a factor of nearly 5X). Flawless cut gems as large as 30-40 carats can be produced on a (somewhat) routine basis). The deposit is extremely large and extremely rich in cuttable feldspar. This material has been given the trade-name GOLDEN SUNSTONE. Another trademarked name, ROYAL SUNSTONE, refers to golden sunstone cut gems larger than 20 carats.

The unique combination of factors indicated above allows for production of cut sunstone with the following parameters:

***unlimited quantity of cut gems possible to meet any conceivable market demand;

***range of sizes from under 1 carat to 100+ carats, all flawless or eye-clean;

***totally uniform color in all sizes and shapes of equal size up to about 25 carats (the large stones appear a bit darker in shade only as a result of greater light absorption due to their greater thickness);

***all gems are essentially flawless and glassy;

The purity of the crystals and their slow, unimpeded growth deep within the earth has allowed these feldspars to attain an internal crystalline perfection unmatched by plagioclase feldspar from any other known locality; with a hardness close to 7 on the Mohs scale. This hardness and structural compactness allows the material to achieve an unusually high degree of polish, comparable to gemstones of hardness 8 and above; however, being feldspar, this material still retains the basic optical properties of the feldspar group, i.e., low refractive index and birefringence. The totally unique combination of low RI and birefringence, combined with extremely high facet surface reflectivity produces a new and previously un-described optical effect that I have termed pseudodispersion

Dispersion is the phenomenon seen in a glass prism and is caused by the bending of light rays of different spectral colors at different angular amounts within a gemstone (best seen in diamond). Dispersion is a measurable quantity and different gems display it to different degrees. The dispersion in cut feldspar is among the lowest of all gemstones.

The amazing thing about golden sunstone, however, is the extremely high polish attainable because of its unusually high degree of hardness. This polish makes such gems remarkably bright. But it ALSO allows the gems to return to the observer's eye colors introduced into the stones as a result of reflection from surrounding objects and light sources. These colors appear to be emanating from within the gemstone itself. The result is a "color play" remarkably similar to the true dispersion so familiar to us in diamond.

Golden sunstone therefore resembles fancy yellow diamond, both in terms of brilliancy and dispersion!

 

 

 

 

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