An agate nodule is a rounded, concentrically banded chalcedony deposit that forms in the vesicles or gas pockets of volcanic rock. Collectors prize it for the colorful, intricate internal banding that is best revealed after slabbing and polishing. It is a staple of lapidary work and turns up globally wherever ancient basaltic lava flows are exposed.
Is this agate nodule?
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 nodule with a known reference. Agate Nodule 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 Nodule leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Agate Nodule 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 Nodule vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside agate nodule
Minerals reported to co-occur with agate nodule. 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
Where rockhounds find agate nodule
5 mapped spotsClassic worldwide localities
- Brazil
- USA (Oregon)
- Mexico
- Uruguay
- Germany
Field-hunting tip
Look in volcanic rocks (basalt/rhyolite) cavities country, the host setting where agate nodule 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.
More agate nodule photos
Common questions
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Find agate nodule on the map
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