Cryptocrystalline sedimentary silica. Flint is the dark variety found in chalk; both were used by early humans for tools. Color: Gray, brown, red, green, black flint. Luster: Waxy to dull. Streak: White. Cleavage: None conchoidal fracture. Hardness: 6.5-7. Transparency: Translucent to opaque. Crystal system: Hexagonal Trigonal. Chemical formula: SiO₂. Specific gravity: 2.60-2.64. Formation: Forms from diagenetic replacement of carbonate sediments by silica from dissolving radiolaria, sponge spicules, or diatoms. Common geological settings: Worldwide; found in limestone and chalk formations as nodules and beds. Common look-alikes and related entries: Chalcedony, Jasper, Obsidian.
Previous: Chalcopyrite — Copper iron sulfide and the most important copper ore mineral. Often confused with pyrite but has a more brassy, often tarnished appearance.
Next: Chlorite — Green phyllosilicate mineral group common in low-grade metamorphic rocks. Gives greenschist its characteristic color.
Chert vs Flint — Compare observable properties and safer field tests.
Jasper vs Chert — Compare observable properties and safer field tests.
Sources, scope & corrections
These authoritative resources support category-level nomenclature, terminology, identification methods, and safety. When a specimen-specific safety warning appears, the public-health source listed here directly supports that precaution. They are not line-by-line citations for every other property on this entry, and natural specimens vary.
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GeoMiner
Last updated
2026-03-30T14:37:42.251053+00:00
Review status
Published; not independently peer-reviewed
IMA–CNMNC List of Mineral Names — International Mineralogical Association. Official mineral-name, nomenclature, and classification records.
Mineral ID Key — Mineralogical Society of America. Physical-property identification methods, repeat-testing guidance, and limitations.
Cryptocrystalline sedimentary silica. Flint is the dark variety found in chalk; both were used by early humans for tools.
How can you identify Chert?
Compare several properties rather than relying on colour alone. This entry records colour: Gray, brown, red, green, black flint; lustre: Waxy to dull; streak: White; Mohs hardness: 6.5-7; cleavage: None conchoidal fracture; crystal system: Hexagonal Trigonal; transparency: Translucent to opaque. Confirm an important identification with additional field tests or qualified laboratory work.
How does Chert form?
Forms from diagenetic replacement of carbonate sediments by silica from dissolving radiolaria, sponge spicules, or diatoms.
Where is Chert commonly found?
Worldwide; found in limestone and chalk formations as nodules and beds.
What is Chert commonly confused with?
Chert may be confused with Chalcedony, Jasper, Obsidian. Compare multiple diagnostic properties because colour and surface appearance can overlap.
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