sedimentary

Chert

Chert (Microcrystalline Quartz)

Hardness: 6.5-7, Color: Brown, tan, gray, Luster: Waxy to dull, Crystal structure: Microcrystalline, Cleavage: None (conchoidal fracture)

Identified June 13, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7, Color: Brown, tan, gray, Luster: Waxy to dull, Crystal structure: Microcrystalline, Cleavage: None (conchoidal fracture)

Forms as chemical sedimentary rock, often from siliceous oozes or replacement of limestone/chalk environments.

Historically used for making stone tools; sometimes used as a decorative stone or in tumbling.

Often called flint when found in chalk deposits. Shows conchoidal fracture which made it ideal for early tool-making.

Identified by its waxy luster, hardness (scratches glass), conchoidal fracture, and lack of cleavage. Common in many sedimentary deposits worldwide.

Sandstone or Siltstone

Arenite (if sandstone)

Sandstone

Arenite (primarily SiO2)

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

Shale or Slaty Mudstone

Argillaceous sedimentary rock

Sandstone

Arenite