Girasol Opal Identification Guide

What Girasol Opal Looks Like

Girasol opal is a translucent, milky-white to faintly bluish common opal that shows a soft, floating blue or whitish sheen (adularescence) which seems to glow from within and move as the stone is turned. Unlike precious opal, it has no flashy play-of-color (no rainbow flecks) — just a gentle, foggy-blue luminosity. Luster is vitreous to slightly waxy, and the body is hazy/cloudy rather than transparent.

Key visual cues

• Milky, translucent body with a soft bluish internal glow
• The sheen "floats" and shifts with the light angle
• No rainbow play-of-color (that distinguishes it from precious opal)
• Glassy luster; often cut as cabochons or spheres

Step-by-Step Field ID Checklist

1. Look for adularescence. Tilt the stone — a hazy blue glow should drift across it.
2. Confirm no play-of-color. Girasol shows sheen, not spectral flashes.
3. Test hardness. Opal is relatively soft (~5.5–6.5); a steel file scratches it.
4. Check translucency. Cloudy, milky, light passes through diffusely.
5. Note density. Opal feels slightly light (~2.0–2.2).
6. Inspect for water sensitivity. Hydrophane behavior (some opals absorb water) can hint at opal rather than quartz.

Diagnostic Tests

• Mohs hardness: ~5.5–6.5 — softer than quartz; will not scratch glass cleanly and can be scratched by a hard steel point. This separates it from girasol quartz (Mohs 7).
• Density: low, ~2.0–2.2 g/cm3 — noticeably lighter than quartz (2.65). A heft/specific-gravity check is one of the best tests.
• Streak: white.
• Fracture: conchoidal; no cleavage.
• Acid: no reaction.
• Optical: amorphous (no birefringence); shows diffuse adularescence, not crisp play-of-color.

Common Look-Alikes and How to Tell Them Apart

• Girasol quartz: also shows a milky bluish floating glow, but quartz is harder (Mohs 7, scratches glass) and denser (2.65). Hardness and weight separate them; the names are often confused in the trade.
• Moonstone: feldspar with a similar blue billowy sheen, but moonstone shows cleavage, a hardness of ~6–6.5, and a more silvery-blue schiller; opal is cleavage-free and softer.
• Precious opal: shows vivid rainbow play-of-color; girasol shows only a soft monochrome sheen.
• Chalcedony/blue opalite (glass): opalite imitation glass often shows an orange glow in transmitted light and a blue glow in reflected light, with bubbles; true girasol opal lacks gas bubbles.
• Hyalite opal: clearer and glassy with possible green fluorescence; girasol is milkier with adularescence.

Where Girasol Opal Is Found

Girasol opal comes from opal-producing regions including Madagascar (a major source of bluish girasol), Mexico, and other common-opal localities. It forms from silica-rich solutions in volcanic and sedimentary host rocks. Look in opal fields where common (non-precious) opal occurs.