Black chert is a microcrystalline variety of silica that typically occurs as nodules within limestone or chalk formations. It is well-known to rockhounders for its conchoidal fracture, which creates exceptionally sharp edges and made it a primary material for prehistoric tool manufacture.
Is this black chert?
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 black chert with a known reference. Black Chert 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. Black Chert leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Black Chert typically shows a waxy luster.
- 4Match the color rangeCompare against the expected color range: black, dark gray.
- 5Look at form & habitCrystal system: trigonal. Typical habit: massive.
Often confused with
Black Chert vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside black chert
Minerals reported to co-occur with black chert. 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
- Opaque
- Crystal system
- Trigonal
- Crystal habit
- Massive
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Decorative, Knapping
- Host rock
- Sedimentary Limestone or Chalk Deposits
- Typical price
- $5-30 per piece
Where rockhounds find black chert
1 mapped spotsClassic worldwide localities
- United Kingdom
- France
- USA
- Denmark
- Belgium
Field-hunting tip
Look in sedimentary limestone or chalk deposits country — that is the host setting where black chert typically forms. If you start seeing calcite, dolomite, chalcedony in float, you are in the right ground. Field specimens usually show a massive habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Virginia — start trip planning there.
Common questions
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Find black chert on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
