Brazilian Opal Identification Guide
How to identify Brazilian opal, including precious play-of-color and crystal opal, and tell it from Australian opal and glass imitations.
Read the full Brazilian Opal encyclopedia entry →
What Brazilian Opal Looks Like
Brazilian opal is hydrated silica opal from Brazil, occurring both as precious opal with play-of-color and as common/crystal opal. Bodies range from milky white and translucent crystal opal to honey, yellow, and pink. Precious Brazilian opal (notably from Piauí) flashes spectral greens, blues, and reds, often in a clean white or clear base. Luster is vitreous to waxy and pieces are transparent to opaque. Some Brazilian opal is hydrophane (it absorbs water and can change transparency when wet).
Step-by-Step Field ID Checklist
- Tilt the stone to look for play-of-color flashes (precious opal) versus a single body color (common opal).
- Note the body color and translucency.
- Check whether it darkens or becomes more transparent when wetted (hydrophane behavior).
- Examine the play-of-color pattern: natural opal shows three-dimensional, directional color.
- Test hardness on an inconspicuous edge.
Key Diagnostic Tests
- Mohs hardness: ~5.5–6.5; relatively soft, scratched by quartz.
- Streak: white.
- Fracture: conchoidal.
- Density: low, SG ~1.9–2.2; opal feels light for its size.
- Play-of-color test: genuine play-of-color shifts with viewing angle and lighting; imitation 'opalescent' glass shows static color or regular flake-like color (e.g., Slocum stone).
- Acid: no reaction.
Common Look-Alikes and How to Tell Them Apart
- Australian opal: mineralogically similar; distinguished by origin and typical matrix (Australian sedimentary vs Brazilian volcanic-hosted). Brazilian precious opal is often more stable and less prone to crazing than some, but both are true opal.
- Opalite/common opal glass imitations: man-made glass with a milky blue-white flash and no genuine directional play-of-color.
- Slocum stone and synthetic opal: show regular, columnar 'lizard-skin' color domains and often gas bubbles.
- Moonstone: shows adularescence (a single floating sheen), not multicolor play-of-color, and is harder (6–6.5) feldspar.
Where Brazilian Opal Is Found
Major sources are Piauí state (Pedro II) for precious white opal and Rio Grande do Sul for common and crystal opal, among others. Brazilian opal occurs in sandstones and volcanic-associated settings.
Frequently asked questions
How can you tell if it's real Brazilian opal?
Genuine opal is soft (5.5–6.5), light (SG under ~2.2), shows conchoidal fracture, and any play-of-color shifts three-dimensionally with angle; imitation glass shows static or flake-like color and may contain bubbles.
What does Brazilian opal look like?
It ranges from milky-white or clear crystal opal to honey and pink common opal, and precious varieties flash green, blue, and red play-of-color in a light base.
Brazilian opal vs Australian opal: what's the difference?
Both are true opal; they are distinguished mainly by origin and host rock, with Brazilian precious opal typically white or crystal opal from Piauí, while Australian opal includes black and boulder types.
Is Brazilian opal hydrophane?
Some Brazilian opal is hydrophane, meaning it absorbs water and can temporarily change transparency or color when wet, so avoid soaking it.