What is Chrysoprase?
Chrysoprase is a green chalcedony variety of quartz, coloured mainly by dispersed nickel and valued as a translucent ornamental and gemstone material.
Mineralogy and structure
The reference formula is SiO2. Chrysoprase belongs to the silicates and has a trigonal crystal system. Chrysoprase does not have a separate species structure: it inherits the microcrystalline quartz structure of chalcedony. Colour can fade with prolonged heat or strong light, so storage should be moderate and protected.
Colour and appearance
Typical colours include apple green, yellow-green, green. Crystal habit, lustre, transparency and matrix association are often as diagnostic as colour.
Formation and localities
Chrysoprase forms in or is associated with near-surface weathering zones and silica-rich fractures associated with nickel-bearing ultramafic rocks. Important documented localities include Western Australia, Poland, Tanzania, Brazil, Kazakhstan and the United States.
Collecting and care
Chrysoprase is best kept as a labelled collector or reference specimen. Protect fragile crystals from impact and prolonged humidity changes. Lead-, arsenic-, chromium- and cobalt-bearing minerals should not be cut, ground or used in jewellery.
