Mint Opal Identification Guide
A field guide to identifying Mint Opal, a pale green common opal, by its waxy luster, light weight, and absence of play-of-color.
Read the full Mint Opal encyclopedia entry →
What Mint Opal Looks Like
Mint Opal is a soft green variety of common opal (often from Peru). It is a gentle, pastel mint-green, usually opaque to translucent, with a smooth waxy surface and no play-of-color (no rainbow flashes), valued for its even, soothing color.
- Color: Pale mint to soft green, sometimes with white or brown matrix mottling.
- Luster: Waxy to subvitreous.
- Transparency: Translucent to opaque.
- Habit/form: Massive, nodular, vein-filling; amorphous hydrated silica.
Step-by-Step Field ID Checklist
- Check for play-of-color: None in common/mint opal — just a steady green body color.
- Look at luster: Waxy/greasy rather than glassy.
- Assess translucency: Soft, diffuse light transmission at thin edges.
- Inspect for matrix: Often hosts brown/black host-rock veining (Andean opal).
- Run hardness, density, and acid tests below.
Key Diagnostic Tests
- Mohs hardness: ~5.5–6.5 — softer than quartz/chalcedony.
- Streak: White.
- Fracture: Conchoidal; no cleavage.
- Density: ~1.9–2.2 g/cm3 — light (hydrated silica).
- Acid: No reaction to dilute HCl.
- Magnetism: None.
Common Look-Alikes and How to Tell Them Apart
- Chrysoprase / green chalcedony: Harder (7), denser, and more vitreous-waxy; mint opal is softer and lighter, and chrysoprase is usually a brighter apple-green.
- Variscite / amazonite: Amazonite is feldspar with cleavage and a blue-green; variscite is greener-blue and slightly harder.
- Green aventurine: Quartz-based, harder, with glittery mica flecks.
- Larimar: Blue-green pectolite with fibrous/needle texture and white veining; mint opal lacks the fibrous pattern.
- Dyed howlite/magnesite: Softer, and magnesite may fizz in warm acid; dyed color concentrates in cracks.
Where It Is Found
Mint/green common opal is best known from the Andes of Peru (Andean opal), with other green common opals from Mexico, the western U.S., and Tanzania.
Frequently asked questions
How can you tell if Mint Opal is real?
Real mint opal is a soft green common opal: waxy luster, hardness ~5.5–6.5, light weight (density under ~2.2), conchoidal fracture, and no fizz in acid. Dye sitting in surface cracks or a much harder, heavier feel suggests an imitation or different stone.
Does Mint Opal have play-of-color?
No. Mint opal is a common (non-precious) opal with a steady green body color and no rainbow play-of-color.
Mint Opal vs chrysoprase — how to tell them apart?
Chrysoprase is chalcedony (hardness 7, heavier, brighter apple-green and more vitreous), while mint opal is softer (5.5–6.5), lighter, and waxier with a paler mint tone.
Where does Mint Opal come from?
Most mint or green common opal on the market is Andean opal from Peru, with additional sources in Mexico, the U.S., and East Africa.