Moss Opal is a variety of common opal that contains internal inclusions of minerals like manganese or iron oxides, which appear as moss-like or dendritic patterns. Collectors should look for specimens with distinct, high-contrast patterns within the translucent, milky-to-clear body of the opal. It is frequently found in cavities or fissures of weathered volcanic rocks where silica-rich fluids have deposited over time.
Is this moss 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 moss opal with a known reference. Moss 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. Moss Opal leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Moss Opal typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: white, clear, green, brown.
- 5Look at form & habitCrystal system: amorphous. Typical habit: massive.
Often confused with
Moss Opal vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside moss opal
Minerals reported to co-occur with moss 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
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Collector, Decorative
- Host rock
- Volcanic Rocks
- Typical price
- $5-50 for small slabs or cabochons
Where rockhounds find moss opal
3 mapped spotsClassic worldwide localities
- USA
- Mexico
- Australia
- Peru
Field-hunting tip
Look in volcanic rocks country — that is the host setting where moss opal typically forms. If you start seeing quartz, chalcedony, clay minerals in float, you are in the right ground. Field specimens usually show a massive habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Kansas, Montana, New Mexico — start trip planning there.
Common questions
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Find moss opal on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
