Chert nodules are hard, concretionary masses of cryptocrystalline silica that typically form within sedimentary layers like limestone or chalk. They are famous for their conchoidal fracture and historically played a vital role in tool making due to their ability to be knapped into sharp edges.
Is this chert 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 chert nodules with a known reference. Chert 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. Chert Nodules leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Chert Nodules typically shows a waxy luster.
- 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 Nodules vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside chert nodules
Minerals reported to co-occur with chert 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
- 2.6-2.65 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
- Typical price
- $5-30 for raw nodules or display specimens
Where rockhounds find chert nodules
4 mapped spotsClassic worldwide localities
- United Kingdom
- France
- United States
- Poland
- Denmark
Field-hunting tip
Look in sedimentary limestone or chalk beds country, the host setting where chert nodules typically forms. If you start seeing calcite, dolomite, chalk in float, you are in the right ground. Field specimens usually show a nodular habit, so 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 nodules photos
Common questions
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Find chert nodules on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
