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Gemstone Family Tree: Chalcedony

Gemstone Family Tree: Chalcedony

Several gems which can lend themselves beautifully to fine jewelry are chalcedony, chrysoprase, agates, and carnelian. There is often confusion about these materials and how they relate to one another, but it's fairly straight-forward. These gemstones are all chalcedony. 

Chalcedony is a cryptocrystalline form of silicate. The term cryptocrystalline refers to the fact that the crystals which comprise the material are so small that they are fairly indeterminate at even a microscopic level. Chalcedony is an extensive family of different materials, and we're going to focus on the varieties I use in fine jewelry.

Agates are a popular form of chalcedony, distinguished by various color patterns or banding.

Chalcedony used in fine jewelry typically refers to the blue to lavender varieties, or to the deep brown to black varieties. A few exceptional deposits of blue to lavender material have been found throughout history, and the deep brown to black material is difficult to source today.

Carnelian is a orangey red to deep red to brown variety of chalcedony, colored by the presence of iron oxides.

Chrome Chalcedony is a green variety of chrysoprase colored by the presence of chromium.

Chrysoprase is a green variety of chalcedony colored by the presence of nickel. The best known source of fine quality chrysoprase is Australia, though Tanzania produces some exceptional material as well.

Gem Silica Chrysocolla is a green-blue variety of chalcedony colored by the presence of copper. The best known deposits of this rare material are from Arizona, USA.