Green Opal Identification Guide
A guide to identifying green opal by its hardness, waxy luster, and water content, and distinguishing common green opal from chrysoprase and serpentine.
Read the full Green Opal encyclopedia entry →
What Green Opal Looks Like
Green opal is a hydrated, amorphous form of silica (SiO2·nH2O), usually a common (potch) opal without play-of-color, colored green by trace nickel or included minerals (such as in Peruvian green opal). It is translucent to opaque with a waxy, resinous, or sub-vitreous luster and a soft, sometimes milky body. Some green opal shows faint opalescence; precious play-of-color is rare in green material.
Step-by-Step Field-ID Checklist
- Note the luster: a waxy-to-resinous sheen rather than a hard glassy quartz shine.
- Test hardness: green opal is softer than quartz—it can be scratched by a steel file/quartz (Mohs ~5.5–6.5).
- Check the fracture: smooth conchoidal fracture, no cleavage.
- Look at translucency: often cloudy/translucent with a gentle inner glow.
- Weigh it: opal feels notably light because of its water content and low density.
Key Diagnostic Tests
- Mohs hardness: 5.5–6.5 (softer than chalcedony)
- Streak: white
- Fracture: conchoidal; no cleavage (amorphous)
- Specific gravity: ~1.98–2.25 (distinctly low—opal feels light)
- No acid reaction; non-magnetic
- Contains 3–10%+ water; some hydrophane opal sticks slightly to the tongue and may darken when wet
Common Look-Alikes and How to Tell Them Apart
- Chrysoprase (green chalcedony): Harder (7) and denser; chrysoprase scratches glass cleanly while opal is softer. Opal's lower SG and waxier feel are key.
- Serpentine: Similar softness but often soapier feel and different green; serpentine is a silicate, opal is hydrated silica with very low SG.
- Green jasper: Opaque and hard (7); jasper does not have opal's translucent glow or low density.
- Variscite: Greener-blue, also low hardness, but distinguished by chemistry and often phosphate associations.
- Glass/opalite: Bubbles and even color; opalite is man-made glass imitating opal.
Where Green Opal Is Found
Green common opal comes from Peru (Andes), Madagascar, Tanzania, Australia, the United States (Oregon, Nevada), and Mexico. It forms from silica-rich groundwater in volcanic and sedimentary settings.
Frequently asked questions
How can you tell if it's real green opal?
Real green opal is relatively soft (Mohs 5.5–6.5), distinctly light in weight (SG around 2), has a waxy-to-resinous luster, conchoidal fracture, and a white streak, often with a milky translucent glow.
What is the difference between green opal and chrysoprase?
Chrysoprase is a green chalcedony with hardness 7 and higher density, while green opal is softer (5.5–6.5), lighter, and has a waxier luster because it is hydrated silica.
What does green opal look like?
It is a translucent to opaque, soft-green stone with a waxy or resinous sheen and a gentle inner glow, usually without the flashing play-of-color of precious opal.
Does green opal have play of color?
Most green opal is common (potch) opal without play-of-color; only rare specimens show the flashing spectral colors associated with precious opal.
Green Opal identified by the community
Recent Green Opal specimens identified with Rock Identifier.
