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Gem Silica or Chrysocolla Chalcedony
| Gem Silica Rough, Arizona
The vivid greenish blue material known as gem silica is quite rare, and high quality specimens are coveted by collectors and jewelry designers. It is also referred to by the names chrysocolla chalcedony and gem silica chrysocolla.
The attraction of this gemstone is its remarkable color. The intense color is due to the presence of copper salts that penetrate the crystal lattice of colorless chalecedony. Though there are other copper-bearing gems that can display a similar color saturation, such as turquoise and chrysocolla, these are much softer stones and are not hard enough for rings. The term "gem" in "gem silica" indicates that this material is gem quality, and in fact it has a hardness of 7 on the Mohs scale and is suitable for all kinds of jewelry, including rings.
Despite the names chrysocolla chalcedony and gem silica chrysocolla, gem silica is not really a form of chrysocolla. Its only connection with chrysocolla is that both minerals are colored by the same copper salts. So the names can be confusing. In fact gem silica is a form of chalcedony, the microscrystalline variety of quartz.
|Gem Silica, Inspiration Mine, Arizona|
Gem silica is found in a just a few locations around the world, including the United States (Arizona and New Mexico), Mexico, Peru, the Philippines and Taiwan. Arizona, a well-known copper-mining region, is generally regarded as yielding the highest quality, with material from the Miami Inspiration mine considered to be the among the very best.
Though most chalcedony varieties such as carnelian and agatge sell for only a few dollars per carat, prices for gem silica can easily reach $50 to $100 a carat, with high grade material selling for over $200 a carat. A top grade specimen would be distinguished by good translucency, consistent and strong color saturation, and the absence of inclusions. Chrysoprase, a bluish-green chalcedony, also carries a premium price in the higher translucent grades.
The demand for gem silica is driven by collectors. Asian buyers have been attracted by gem silica's similarity to some forms of jade.