Common opal is a non-precious variety of opal that lacks the characteristic play-of-color found in precious opal. It is typically found in massive or botryoidal forms and is often cut into cabochons for jewelry or collected for its diverse, solid color palette.
Is this common 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 common opal with a known reference. Common 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. Common Opal leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Common Opal typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, gray, yellow, brown, green, pink, blue.
- 5Look at form & habitCrystal system: amorphous. Typical habit: massive, botryoidal, reniform, stalactitic.
Often confused with
Common Opal vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside common opal
Minerals reported to co-occur with common 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
- Translucent
- Crystal system
- Amorphous
- Crystal habit
- Massive, Botryoidal, Reniform, Stalactitic
- Cleavage
- None
- Fluorescence
- Green or White Under UV
- Rarity
- Common
- Uses
- Lapidary, Collector, Decorative
- Host rock
- Volcanic Ash, Sedimentary Rocks, Hydrothermal Veins
- Typical price
- $5-50 for specimens, $10-100 for cut material
Where rockhounds find common opal
16 mapped spotsClassic worldwide localities
- Australia
- Mexico
- USA
- Peru
- Ethiopia
U.S. states with common opal
Each link opens a state-specific list of mapped rockhounding spots that produce common opal.
Field-hunting tip
Look in volcanic ash, sedimentary rocks, hydrothermal veins country — that is the host setting where common opal typically forms. If you start seeing quartz, chalcedony, montmorillonite in float, you are in the right ground. Field specimens usually show a massive, botryoidal, reniform, stalactitic habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in New Jersey, Nevada, North Carolina — start trip planning there.
Common questions
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Find common opal on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
