Gem of the Month

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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September, 2002

Chrysocolla

The pure mineral, chrysocolla, is found in oxidized zones of copper deposits as a powdery crust on rock surfaces or as tiny crystal aggregates. It is extremely soft and brittle and never occurs in cuttable crystals, so why consider it a gem? Chrysocolla has one big thing to recommend it -- color. The saturated greenish blue to blue-green to bluish green color is unlike that found in any other material. But it is only when chrysocolla is mixed with other copper minerals and/or quartz that it is interesting to the gem collector and jewelry lover. In combination with malachite, azurite, cuprite, turquoise or most notably, quartz, it attains the stability needed to be worked as a gem. The hardness and degree of polish such a combination can achieve is largely dependent on the amount of quartz in the mix, or in other words, how silicified (or silicated) it is. The epitome of this is seen in "gem silica", more properly called chrysocolla chalcedony, when tiny chrysocolla crystals are found throughout quartz creating a uniform blue green color. This glowing blue green gem is as hard and durable as any other chalcedony.

Chrysocolla deposits and those of its mixtures with other minerals, are found wherever copper mining occurs: for example, in the Western USA, Russia, Zaire, and Chile. An obsolete synonym for chrysocolla is Bisbeeite, which no doubt arose in reference to the big copper mining operation in the Arizona town of that name. Other than "gem silica", there aren't a lot of individual variety names given to the various mixtures, but one notable exception is Eliat stone, a turquoise/chrysocolla/malachite mix found in Israel. Gems of some of the softer chrysocolla mixtures are often sold as doublets with agate bases for stability and sometimes are stabilized with resins to improve durability. Parrot wing jasper gets some of its beautiful color from chrysocolla inclusions. Drusy "chrysocolla" is actually silicated chrysocolla with a crust of colorless quartz crystals and would more properly, perhaps,be called drusy gem silica.

Except for gem silica, chrysocolla gems need to be treated with care and are not good choices for rings, belt buckles or bracelets. The large sizes they often come in, though, lend themselves admirably to the brooches, bolos and pendants for which they are best suited.

Get some color in your life! Think chrysocolla.


Value Considerations

Value in chrysocolla pieces is related to color, pattern and degree of silification, with more intensely colored, pleasingly patterned, harder pieces at a premium. The most valuable variety is gem silica, with top prices obtained for pieces of highest translucency and even, saturated color. Druzies are also at the higher end of the value scale. A modifying factor, as for any material, would be the quality of the cutting or carving and the degree of polish. For the most part, price per carat doesn't escalate greatly with size.
Gemological Properties:

Makeup: Hydrated Copper Silicate

Hardness: 2 - 4 (up to 7 if highly silicified)

Toughness: Good if silicated, brittle otherwise

RI: 1.57 -1.63

SG: 2.0 - 2.4

Cleavage: none

Fluorescence: none

Luster: Greasy to vitreous (depending on degree of silicification)
Stones Currently Available:

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Go to: Homepage -- what's new in faceted gems -- what's new in designer cabochons and gem carvings -- gem of the month -- gem of the month archive -- birthstone of the month -- key to all the codes used on the ACS site -- definitions of terms used on the ACS site -- how to order -- about ACS -- about the ACS cutters -- settings for these gems --faceting information -- purchase UltraTec equipment