A chalcedony nodule typically forms as a rounded, botryoidal mass within a rock cavity or as a sedimentary concretion. It is recognized by its waxy luster, the absence of crystalline structure visible to the naked eye, and its characteristically smooth, mammillary surface.
Is this chalcedony 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 chalcedony nodule with a known reference. Chalcedony 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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: waxy.
- 4Match the color rangeCompare against the expected color range: white, gray, blue, brown, tan.
- 5Look at form & habitCrystal system: trigonal. Typical habit: botryoidal.
Often confused with
Chalcedony Nodule vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads waxy on Chalcedony Nodule and vitreous to dull on Opal.
How to tell apart: Chalcedony Nodule is noticeably harder (Mohs 6.5-7 vs. 4-4.5); luster reads waxy on Chalcedony Nodule and vitreous, may be pearly on Smithsonite.
How to tell apart: Luster reads waxy on Chalcedony Nodule and vitreous, weak pearly on {001} on Prehnite.
Often found alongside chalcedony nodule
Minerals reported to co-occur with chalcedony 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
- 2.6-2.65 g/cm³
- Streak
- White
- Luster
- Waxy
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Botryoidal
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Collector, Decorative
- Host rock
- sedimentary and volcanic cavities
Where rockhounds find chalcedony nodule
2 mapped spotsClassic worldwide localities
- USA
- Mexico
- Brazil
- India
- Madagascar
Field-hunting tip
Where it forms: sedimentary and volcanic cavities. If you start seeing quartz, calcite, goethite in float, you are in the right ground. Typical habit: botryoidal. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Tennessee, Washington. Start trip planning there.
More chalcedony nodule photos
Common questions
How do you identify chalcedony nodule?+
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Find chalcedony nodule on the map
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