- Chalcedony displays a waxy, dull or glossy luster, which may be semitransparent to translucent, and can assume a wide range of colors. The most common colors are white to grey, blue-gray or shades of brown from pale to almost black.
- The chemical formula for chalcedony is silicon dioxide (SiO2) or silica. Thought to be a fibrous form of cryptocrystalline quartz, chalcedony has more recently shown to contain moganite, a monoclinic polymorph of quartz. The crystal structures of the minerals differ; quartz crystals are trigonal, whereas the structure of moganite is monolithic.
- Microcrystalline chalcedony has twice the solubility of quartz, despite the two minerals being chemically identical, according to the National Academy of Sciences. Soluble minerals such as silica is what form petrified wood.
- A diverse ornamental stone, varieties include agate, chrysoprase, tiger's eye, bloodstone, jasper and moss agate and are used in carving cabochons and beads. The distinct apple-green color of chrysoprase commends a higher price than other varieties.
Agate, the most diverse and popular of all chalcedony, it is especially abundant, creating a wide array of stunning examples. In its natural state, agate is unattractive; however, trimmed and polished specimens reveal its striking beauty.
A well-known example of chalcedony is petrified wood--wood that has been completely transformed into silica (or another mineral), called petrifaction or silicification. Chalcedony occasionally occurs in geodes, lining the cavity with the silica mineral. - Yuma points, or Eden points, found in Northeastern Colorado, were first used from 10,000 to 5,000 B.C., and generally made of flint, a high-quality chalcedony harder than surgical steel scalpels. Flint, or flintstone, mainly occurs in sedimentary rocks, such as limestone and chalk. Other forms of chalcedony used for tools and arrowheads include obsidian, agate, petrified wood and jasper.
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