A dark body tone turns black opal into a stage for moving colour. Against that deeper background, flashes of red, green, blue, and orange can appear sharper and more dramatic than they do in lighter opal varieties.

Boulder Opal earns attention when light begins to travel across or through it. That combination of multicolour body colour, opalescence, play of colour, iridescence optical effects, and 5.5 Mohs hardness is what usually makes it recognisable in practice. The effect is best judged in motion, since a static view rarely shows the full character of the stone.

Crystal Opal earns attention when light begins to travel across or through it. That combination of multicolour body colour, opalescence, play of colour, iridescence optical effects, and 5.5 Mohs hardness is what usually makes it recognisable in practice. The effect is best judged in motion, since a static view rarely shows the full character of the stone.

Ethiopian Opal profile is under factual gemological review. Properties shown here are provisional unless marked as verified.

Mexican Opal profile is under factual gemological review. Properties shown here are provisional unless marked as verified.

Opal is less about crystal form than about light. Depending on structure, it may show a soft inner haze, bold flashes of spectral colour, or a calm body tone that changes character as the stone is turned in the hand.

The appeal of Peruvian Blue Opal lies in what happens after the stone is turned in the light. That combination of blue body colour, opalescence, play of colour, iridescence optical effects, and 5.5 Mohs hardness is what usually makes it recognisable in practice. The effect is best judged in motion, since a static view rarely shows the full character of the stone.