Madagascar Opal Identification Guide

What Madagascar Opal Looks Like

Madagascar produces both precious opal (with play-of-color) and abundant common opal (potch), including green and pastel "opalized" material. Opal is hydrated amorphous silica.

• Color: body color ranges from white, cream, green, blue, to pink; precious material flashes spectral play-of-color
• Luster: waxy to vitreous; resinous on fracture
• Transparency: transparent (jelly) to opaque
• Habit: amorphous — nodules, seams, and masses; no crystal faces

Step-by-Step Field ID Checklist

1. Tilt the stone in light — if you see shifting rainbow flashes (play-of-color), it is precious opal; steady single color is common opal.
2. Check the luster — waxy/resinous glassy surface typical of opal.
3. Test hardness — relatively soft, Mohs 5.5-6.5; quartz scratches it.
4. Note conchoidal fracture and lack of cleavage.
5. Watch for hydrophane behavior — some Madagascar opal is porous and turns more transparent (and can stick to the tongue) when wet.

Key Diagnostic Tests

• Mohs hardness: 5.5-6.5 — softer than quartz and most gem silica.
• Streak: white.
• Cleavage: none; conchoidal fracture.
• Specific gravity: low, ~1.9-2.2 (opal is water-bearing and light).
• Hydrophane test: porous opal absorbs water, changing transparency.

Common Look-Alikes and How to Tell Them Apart

• Chalcedony/agate: harder (7), denser, no play-of-color, not hydrophane.
• Glass/opalite (man-made): opalite shows a milky blue glow but no true spectral play-of-color and often has bubbles.
• Moonstone: shows adularescence (a single sheen) not multi-colored play-of-color, and is harder feldspar.
• Plastic imitation opal: very light, warm to touch, soft; "play" looks too regular/columnar (lab opal "lizard skin").

Where It Is Typically Found

Madagascar opal comes from several deposits across the island; well-known green common opal and some precious opal occur in the central highlands. Most material reaches the market as nodules and rough seams.