Chalcedony

Chalcedony is the form of Quartz that is compact and microcrystalline. It occurs in many different forms, colors, and patterns, and many varieties have been used as gemstones since antiquity. In the gemstone trade, the term Chalcedony is often used specifically to describe the white, gray, or blue translucent type of Chalcedony, but its technical term includes all additional varieties.

Chalcedony is found in all types of colors, and its varieties are named based on color. The variety Agate is a multicolored form, well known for its distinctive banding patterns. Some forms of Chalcedony, such as Chrysoprase, are intensely colored, while others are light. In blue Chalcedony, the deeper the color, the more desirable the gemstone. The classic Chalcedony varieties are described below:

Agate
Multicolored banded variety, and the most well-known and unique form of Chalcedony. Agate itself has many different known varieties. All Agates contain distinctive patterns, which make each Agate different from the next. See the Agate gemstone page for more details.

Aventurine
Opaque, compact form, most often green in color, containing small Mica, Hematite, or Goethite scales which cause a glistening effect. See the Aventurine gemstone page for more details.

Bloodstone
Dark green to greenish blue variety speckled with red or brown spots. See the Bloodstone gemstone page for more details.

Carnelian
Red to amber-red translucent variety. Some forms of Carnelian are heat treated to darken the lighter tones. See the Carnelian gemstone page for more details.

Chrysoprase
Apple green variety; one of the more popular gemstone forms of Chalcedony. See the Chrysoprase gemstone page for more details.

Jasper
Opaque form of brown, often multicolored, spotted, or speckled. See the Jasper gemstone page for more details.

Onyx
May describe solid black Chalcedony, banded black and white Chalcedony (usually in parallel banding), or any Chalcedony with a black base and white upper layer. See the Onyx gemstone page for more details.

Sard and Sardonyx
Sard is the brownish to brownish-red, transparent to translucent variety. The related Sardonyx has parallel bands of brownish to red alternating with white or sometimes black bands.

Tiger's Eye
Pseudomorph of compact Quartz after the fibrous mineral Crocidolite. Tiger's Eye is famous for its chatoyant effect and glistening sheen. See the Tiger's Eye gemstone page for more details.