chrysoprase

The apple-green form of chalcedony.

Chrysoprase (also chrysophrase) is a gemstone variety of chalcedony (fibrous form of quartz) that contains small quantities of nickel. This sets it apart from rock crystal, amethyst, citrine, and the other varieties of crystalline quartz which are basically transparent and formed from easily recognized six-sided crystals. Unlike many non-transparent members of the quartz family, it is the color of chrysoprase, rather than any pattern of markings, that makes it desirable.

Due to its comparative scarcity and pleasing green color, chrysoprase is one of the most prized varieties of quartz.

Unlike emerald which owes its beautiful green color to the presence of chromium, the color of chrysoprase is due to trace amounts of nickel in the structure. Chrysoprase results from the deep weathering or lateritization of nickeliferous serpentinites or other ultramafic ophiolite rocks. In the Australian deposits, chrysoprase occurs as veins and nodules with brown goethite and other iron oxides in the magnesite-rich saprolite below an iron and silica cap.

As with all forms of quartz, chrysoprase has a hardness of 6 - 7 on the Mohs hardness scale and a conchoidal fracture like flint.

The best known sources of chrysoprase are Queensland, Western Australia, Germany, Poland, Russia, Arizona, California, and Brazil.