A chert nodule is a hard, concretionary mass of cryptocrystalline silica that forms within sedimentary layers such as limestone or chalk. It is known for its conchoidal fracture and historically played a vital role in tool making, since it can be knapped to a sharp edge.
Is this chert 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 chert nodule with a known reference. Chert 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: gray, brown, black, white, tan.
- 5Look at form & habitCrystal system: trigonal. Typical habit: nodular.
Often confused with
Chert Nodule vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside chert nodule
Minerals reported to co-occur with chert 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
- Nodular
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Collector, Decorative
- Host rock
- sedimentary limestone or chalk beds
Where rockhounds find chert nodule
4 mapped spotsClassic worldwide localities
- United Kingdom
- France
- United States
- Poland
- Denmark
Field-hunting tip
Where it forms: sedimentary limestone or chalk beds. If you start seeing calcite, dolomite, chalk in float, you are in the right ground. Typical habit: nodular. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Missouri, West Virginia. Start trip planning there.
More chert nodule photos
Common questions
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Find chert nodule on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
