Each month this section will feature either a topic of interest to gem lovers or one special gemstone with background on the material and its value.

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Often called "Gem Silica" in the trade, this material is more correctly referred to as chrysocolla chalcedony. Essentially it is near colorless chalcedony that has been stained by infiltration of solutions carrying the same copper salts which color chrysocolla. If it is evenly stained throughout, it has an intense, uniform, slightly to moderately greenish blue color. Chrysocolla itself, though beautiful in color, is far too soft (H = 2- 4) to be used for jewelry, but as this material is chalcedony with a hardness of 7, it is quite suitable. Sources include, Arizona, New Mexico, Mexico, Taiwan and the Philippines. Rarely gem silica occurs in a drusy form.

[Drusy Gem Silica]

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The most valuable specimens of this kind of material are those that are highly translucent, evenly colored, free from inclusions and strongly saturated in color. People who may not realize how rare such stones are, sometimes are taken aback by the relatively high price for what is afterall, a form of quartz and a cabochon stone to boot. Increased demand and familiarity with this gem has been occasioned by top gem carvers and goldsmiths recently making this stone a "gem of choice". There has also been intense interest by Oriental collectors which has driven prices up as well. Those specimens which tend to greenish hues and which are opaque, included or uneven are much less costly.

Gemological Data:

Makeup: microcrystalline or cryptocrystalline quartz, Si0₂

Luster: vitreous

Hardness: 7

Crystal structure: hexagonal

Fracture: conchoidal to granular

Density: 2.60

RI: 1.54

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