Green Opal

Green opal is a variety of common opal (without play-of-color) whose green color comes from trace transition-metal impurities, chiefly nickel (as in prase opal) or chromium. It ranges from soft apple green to deeper olive and moss tones, often with mottling or inclusions.

Most green opal is opaque to translucent and is cut into cabochons, beads, and carvings rather than faceted. It is an affordable, attractive ornamental gem widely used in artisan jewelry.

Major sources include Madagascar, Peru, and Tanzania, with chromium-rich green opal (chrome chalcedony's opal cousin) from East Africa.

Green opal forms like other common opal, by deposition of hydrated silica from groundwater in weathered volcanic and sedimentary rocks at low temperatures. The green coloration arises when the silica incorporates trace nickel or chromium derived from nearby ultramafic or mineralized rocks.

Prase opal, a nickel-bearing green opal, is associated with weathered nickel-laterite deposits, such as those in Tanzania and Poland (Szklary). Madagascan green opal forms in sedimentary and volcanic settings.

As an amorphous mineraloid, it requires stable near-surface conditions and a steady silica supply over time.

Look for an opaque to translucent green stone with a waxy to vitreous luster, white streak, and Mohs hardness near 5.5-6.5 (softer than quartz). Color is often uneven or mottled with brown or white veining.

Look-alikes: Chrysoprase is a green chalcedony but harder (around 6.5-7) and does not craze. Variscite is greener-blue and similar softness but a phosphate. Serpentine is softer and greasier. Aventurine quartz is harder with sparkly inclusions.

Green opal's lower hardness, possible crazing, and lack of crystalline structure help separate it from chalcedony and quartz look-alikes.

Green opal is used in cabochons, beads, pendants, and carvings for affordable fashion and artisan jewelry. Its soothing color makes it popular in bohemian and nature-themed designs.

It has no significant industrial use. Metaphysically it is associated with the heart chakra, emotional renewal, and balance, though these are not scientific claims.

As with all opal, green opal should be protected from impacts and drying to avoid crazing; it is best in pendants and earrings rather than everyday rings.