sedimentary

Chert (often referred to as Flint)

Chert (Microcrystalline Quartz, SiO2)

Hardness: 7 on Mohs scale; Color: Variable (tan, grey, brown, or black as shown); Luster: Waxy to dull; Crystal structure: Cryptocrystalline (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Variable (tan, grey, brown, or black as shown)
Luster: Waxy to dull

Identified March 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or shale beds. Often found in nodules or bedded layers.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges; modern uses include construction aggregate, road surfacing, and as a component in ceramics or glass.

Geological facts

Chert was one of the most important minerals for early humans, used to create arrowheads, scrapers, and fire-starting tools. Its ability to produce fire when struck against steel led to the creation of 'flintlock' mechanisms.

Field identification & locations

Identify by its 'shell-like' conchoidal fracture patterns and the fact that it will easily scratch glass. Commonly found in riverbeds, chalk deposits, or as nodules in weathered limestone fields. Collectors look for unique color patterns like 'Banded Chert'.

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Sandstone or Siltstone

Arenite (if sandstone)

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Sandstone

Arenite (primarily SiO2)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone (Quartz-rich)

Arenite (SiO2)

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Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

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