Agate nodules are rounded, concentrically banded chalcedony deposits that form in the vesicles or gas pockets of volcanic rocks. Collectors prize them for their colorful, intricate internal banding patterns which are best revealed after slabbing and polishing. They are a staple of lapidary work and can be found globally in regions with ancient basaltic lava flows.
Is this agate nodules?
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 agate nodules with a known reference. Agate Nodules 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. Agate Nodules leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Agate Nodules typically shows a waxy luster.
- 4Match the color rangeCompare against the expected color range: banded, white, gray, blue, red, yellow, brown.
- 5Look at form & habitCrystal system: trigonal. Typical habit: nodular, botryoidal, banded fillings in cavities.
Often confused with
Agate Nodules vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside agate nodules
Minerals reported to co-occur with agate nodules. 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
- 2.59-2.61 g/cm³
- Streak
- White
- Luster
- Waxy
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Nodular, Botryoidal, Banded Fillings in Cavities
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Collector, Decorative
- Host rock
- Volcanic Rocks (basalt/rhyolite) Cavities
- Typical price
- $5-50 for small polished pieces, up to $200 for large display nodules.
Where rockhounds find agate nodules
3 mapped spotsClassic worldwide localities
- Brazil
- USA (Oregon)
- Mexico
- Uruguay
- Germany
Field-hunting tip
Look in volcanic rocks (basalt/rhyolite) cavities country — that is the host setting where agate nodules typically forms. If you start seeing quartz, calcite, zeolites in float, you are in the right ground. Field specimens usually show a nodular, botryoidal, banded fillings in cavities habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Michigan, Oregon, Pennsylvania — start trip planning there.
Common questions
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Find agate nodules on the map
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