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.Īs with all forms of chalcedony, chrysoprase has a hardness of 6 to 7 on the Mohs hardness scale and a conchoidal fracture like flint. Chrysoprase results from the deep weathering or lateritization of nickeliferous serpentinites or other ultramafic ophiolite rocks. The nickel reportedly occurs as different silicates, like kerolite or pimelite (not NiO mineral, bunsenite, as was reported before). Unlike emerald which owes its green color to the presence of chromium, the color of chrysoprase is due to trace amounts of nickel compounds in the form of very small inclusions. The word chrysoprase comes from the Greek χρυσός chrysos meaning 'gold' and πράσινον prasinon, meaning 'green'. Unlike many non-transparent silica minerals, it is the color of chrysoprase, rather than any pattern of markings, that makes it desirable. Other members of the cryptocrystalline silica family include agate, carnelian, and onyx. This sets it apart from rock crystal, amethyst, citrine, and the other varieties of crystalline quartz. ![]() ![]() (However, the term prase is also used to describe chlorite-included quartz, and to a certain extent is a color-descriptor, rather than a rigorously defined mineral variety.)Ĭhrysoprase is cryptocrystalline, which means that it is composed of crystals so fine that they cannot be seen as distinct particles under normal magnification. ![]() The darker varieties of chrysoprase are also referred to as prase. Its color is normally apple-green, but varies to deep green. Chrysoprase, chrysophrase or chrysoprasus is a gemstone variety of chalcedony (a cryptocrystalline form of silica) that contains small quantities of nickel.
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