Crystal opal is a transparent to semi-transparent variety of precious opal renowned for its brilliant internal play-of-color resulting from the diffraction of light by microscopic silica spheres. Unlike common opal, it exhibits a distinct spectral flash when rotated and is highly prized for its clarity and brightness. Collectors should examine the stone against a light source to verify transparency and look for sharp, multi-colored 'fire' patterns.
Is this crystal opal?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch crystal opal with a known reference. Crystal Opal sits at Mohs 5.5-6.5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Crystal Opal leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Crystal Opal typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, black, colorless, blue, green, yellow, red, orange.
- 5Look at form & habitCrystal system: amorphous. Typical habit: nodular, botryoidal, reniform, massive.
Often confused with
Crystal Opal vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside crystal opal
Minerals reported to co-occur with crystal opal. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- SiO₂·nH₂O
- Mohs hardness
- 5.5-6.5
- Density
- 1.9-2.2 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Amorphous
- Crystal habit
- Nodular, Botryoidal, Reniform, Massive
- Cleavage
- None
- Fluorescence
- Often Fluorescent White, Green, Or Yellow Under UV
- Rarity
- Rare
- Uses
- Gemstone, Jewelry, Collector
- Host rock
- Sedimentary Ironstone, Volcanic Rhyolite, Or Sandstone Cavities
- Typical price
- $50-500 per carat depending on play-of-color and intensity
Where rockhounds find crystal opal
Classic worldwide localities
- Coober Pedy, Australia
- Lightning Ridge, Australia
- Welo, Ethiopia
- Queretaro, Mexico
- Virgin Valley, USA
Field-hunting tip
Look in sedimentary ironstone, volcanic rhyolite, or sandstone cavities country, the host setting where crystal opal typically forms. If you start seeing quartz, montmorillonite, limonite in float, you are in the right ground. Field specimens usually show a nodular, botryoidal, reniform, massive habit, so train your eye for that shape before scanning the outcrop.
More crystal opal photos
Common questions
How do you identify crystal opal?+
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Find crystal opal on the map
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