sedimentary

Chert (specifically Flint)

Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Dark grey to black with possible tan/brown weathering; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Dark grey to black with possible tan/brown weathering
Luster: Waxy to vitreous

Identified March 8, 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 fluids in sedimentary limestone/chalk beds. It can date from the Precambrian to recent times.

Uses & applications

Historically used for stone tools and starting fires (flint and steel). Modernly used in road construction, as jewelry (if colorful), and as a grinding medium in ball mills.

Geological facts

One of the oldest materials used by humans for toolmaking due to its predictable conchoidal fracture which creates razor-sharp edges. It was a primary trade commodity in the Stone Age.

Field identification & locations

Identify in the field by its characteristic 'shell-like' curved fractures and its ability to scratch glass easily. Commonly found in riverbeds, glacial deposits, or embedded in limestone outcrops. Collectors often look for worked edges indicating prehistoric artifacts.

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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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