Montana Moss Agate is a highly sought-after chalcedony characterized by distinct dendritic inclusions of manganese and iron oxides that resemble moss or fern patterns. It is typically found as water-worn cobbles in the gravel beds of the Yellowstone River and its tributaries. Collectors prize it for its high transparency and the intricate, landscape-like imagery within the stone.
Is this montana moss agate?
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 montana moss agate with a known reference. Montana Moss Agate sits at Mohs 6.5-7 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Montana Moss Agate leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Montana Moss Agate typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: clear, white, gray, brown, red.
- 5Look at form & habitCrystal system: trigonal. Typical habit: massive.
Often confused with
Montana Moss Agate vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside montana moss agate
Minerals reported to co-occur with montana moss agate. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- SiO₂
- Mohs hardness
- 6.5-7
- Density
- 2.6 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Massive
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Collector, Decorative, Jewelry
- Host rock
- Alluvial Gravels and River Deposits
- Typical price
- $5-50 rough, $20-200 polished specimen
Where rockhounds find montana moss agate
3 mapped spotsClassic worldwide localities
- Yellowstone River, Montana, USA
- Glendive, Montana, USA
- Miles City, Montana, USA
Field-hunting tip
Look in alluvial gravels and river deposits country — that is the host setting where montana moss agate typically forms. If you start seeing quartz, jasper, calcedony 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 North Dakota — start trip planning there.
Common questions
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Find montana moss agate on the map
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