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, 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.
More moss opal photos
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.
