Chrysoprase

Chrysoprase is the bright apple-green to deep-green variety of chalcedony, a microcrystalline form of quartz. Unlike most green stones, its color comes from trace nickel rather than chromium or iron, giving it a uniquely fresh, even green.

It is the most valued of the green chalcedonies and is sometimes marketed misleadingly as "Australian jade," since fine material comes from Queensland, Australia. Its color can fade with prolonged heat or strong sunlight.

Translucent, fine-grained, and free of banding in top grades, chrysoprase takes an excellent polish and has been used as a gemstone since antiquity.

Chrysoprase forms in the weathered, near-surface zones of nickel-rich ultramafic rocks such as serpentinites. As these rocks break down, nickel is released and incorporated into silica-rich groundwater.

The nickel-bearing silica then precipitates as chalcedony in cracks, cavities, and seams within the weathered rock (laterite), producing the characteristic green color. The coloring agent is finely dispersed nickel minerals.

Major deposits occur in Queensland, Australia (notably Marlborough), as well as Poland (the historic Szklary deposit), Tanzania, Brazil, and the United States. Chrome-bearing green chalcedony from Zimbabwe is sold separately as mtorolite.

Look for a translucent, even apple-green to mint-green stone with a smooth waxy-to-glassy luster and no obvious crystals (it is microcrystalline). It is hard (6.5-7) and scratches glass; streak is white.

Unlike jade (jadeite or nephrite), chrysoprase is a quartz, so it is slightly different in heft and lacks jade's fibrous toughness; a refractive index and density test separate them. It does not fizz in acid, unlike green calcite.

Beware dyed green chalcedony or agate imitations: natural chrysoprase shows even color throughout and may have subtle cloudy zoning, whereas dyed stones often show color concentrated in cracks. Distinguish from chrome chalcedony (mtorolite), which is colored by chromium.

Chrysoprase is a prized gemstone used in rings, pendants, earrings, beads, and cabochons. Its durability (hardness near 7) makes it suitable for everyday jewelry, and fine even-green material commands high prices.

Historically it was popular in Roman, medieval, and Art Nouveau jewelry, and was reputedly a favorite of Frederick the Great. It is also carved into ornamental objects and inlays.

Metaphysically it is associated with the heart, growth, and optimism; these are spiritual beliefs rather than scientific facts. Care should be taken to avoid prolonged heat and sunlight, which can fade its nickel-derived color.