Blue chert is a microcrystalline form of quartz known for its smooth, waxy luster and conchoidal fracture. It is typically found as nodules within sedimentary rocks like limestone or chalk and is highly prized by lapidaries for its hardness and striking blue hues.
Is this blue 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 blue chert with a known reference. Blue 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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: waxy.
- 4Match the color rangeCompare against the expected color range: blue, gray-blue, light blue.
- 5Look at form & habitCrystal system: trigonal. Typical habit: massive.
Often confused with
Blue Chert vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside blue chert
Minerals reported to co-occur with blue 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
- 2.6-2.7 g/cm³
- Colors
- Streak
- White
- Luster
- Waxy
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Massive
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Decorative, Collector
- Host rock
- sedimentary
Where rockhounds find blue chert
1 mapped spotsClassic worldwide localities
- USA
- United Kingdom
- Brazil
- Mexico
Field-hunting tip
Where it forms: sedimentary. If you start seeing calcite, quartz, dolomite in float, you are in the right ground. Typical habit: massive. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Missouri. Start trip planning there.
More blue chert photos
Common questions
How do you identify blue chert?+
Where is blue chert found?+
Can I find blue chert in the United States?+
What rocks look like blue chert?+
What minerals are found with blue chert?+
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What is blue chert used for?+
Find blue chert on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
