Chrysoprase

Hardness: 6.5-7 on Mohs scale. Color: Apple-green to deep green, due to nickel impurities. Luster: Vitreous to waxy. Crystal Structure: Trigonal (microcrystalline aggregates). Cleavage: None (fractures conchoidally). Specific Gravity: 2.58-2.64. Typically translucent to opaque.

Chrysoprase forms in veins and nodules in serpentinites or other ultramafic rocks that have undergone deep weathering and laterization. It is often found in association with magnesite and other nickel-bearing minerals. Its formation is typically associated with hydrothermal processes and the supergene enrichment of nickel, often occurring in relatively shallow depths. Geological age varies depending on the host rock and specific tectonic events, but it forms in environments where nickel-rich fluids interact with silica-rich solutions, often secondary deposits.

Prized as a gemstone, particularly for cabochons, beads, and carved ornamental objects. Its appealing green color makes it a popular choice for jewelry. Historically, it was used by the Greeks and Romans for seals and other decorative purposes. Due to its hardness, it can be polished to a high sheen.

The name 'chrysoprase' comes from the Greek words 'chrysos' meaning 'gold' and 'prason' meaning 'leek,' referring to its golden-green color. It was a favorite gemstone of Frederick the Great of Prussia. Unlike emerald, whose green color comes from chromium, chrysoprase gets its color from trace amounts of nickel. It is a more affordable alternative to jade for jewelry.

In the field, chrysoprase can be identified by its distinctive vibrant apple-green to deep green color, its waxy to vitreous luster, and its hardness (it will scratch glass). It typically occurs as cryptocrystalline masses, not well-formed crystals. Common locations include Australia (especially Queensland, regarded as the world's best source), Germany (Silesia, historically significant), Russia (Urals), Brazil, Poland, and the United States (California, Oregon, Arizona). Collectors look for even, saturated color and good translucency. Distinguished from jade by its conchoidal fracture and harder nature (jade is typically 6-6.5).