The name crystal stone chrysoprase comes from the Greek chyros, meaning “golden,” and prason, “leek,” which describes the color of the stone. Across the years, this name was applied to several yellowish green gemstones, including beryl, but eventually it became limited to the apple-green, microcrystalline variety of chalcedony. Crystal stone chrysoprase comes from the class of framework silicates with trigonal crystal system. It is composed by silicon dioxide. The hardness is stopped at level 6.5. Crystal stone chrysoprase has vitreous to resinous luster and conchoidal fracture. The duller, leek-green stones have been called prase instead. The habit is massive, or as veins in rock. Crystal stone chrysoprase is found mostly in Australia, although it has been found in Brazil and the Ural Mountains in Russia and in Austria.
Crystal stone chrysoprase is usually translucent, but poorer quality stones may appear opaque. A small number of crystal stone chrysoprases are semitransparent and even transparent. It has none cleavage. If the color is good, these stones fetch a high price. Crystal stone chrysoprase is usually fashioned into cabochons, beads, and bangles, or it is carved to create jewelry and other ornamental objects. It is easily worked and takes a fine polish. The highest-quality material is a rich, evenly colored apple green, and does not contain any flaws, inclusions, or imperfections. Common colors are pale green, yellowish green, and deep green. Crystal stone chrysoprase is among the most valuable of the chalcedonies. The dispersion is 0.013 and the specific gravity is in between 2.57-2.64.
Crystal stone chrysoprase is cryptocrystalline, that is, it has a microscopic crystalline structure. Under high magnification, these crystals look like parallel fibers. The refractive index of crystal stone chrysoprase is 1.530-1.538 and the birefringence is up to 0.004. Unlike most other green stones, which derive their color from chromium or vanadium, crystal stone chrysoprase’s distinctive green color is the result of included oxidized nickel compounds, such as nickel silicate clay minerals. A rare, related chalcedony in darker, more vibrant shades of green is colored by chromium, it occurs in Zimbabwe and is called mtorolite, but is sometimes sold as “chrome chalcedony”, one of the quite antique natural gemstones.
