sedimentary

Chert (Nodule)

Microcrystalline Quartz (SiO2)

Hardness: 6.5–7 (Mohs); Color: Brown, red, tan, or gray; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Hardness: 6
Color: Brown, red, tan, or gray
Luster: Waxy to dull

Identified June 29, 2026More sedimentary →

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Physical properties

Hardness: 6.5–7 (Mohs); Color: Brown, red, tan, or gray; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation within limestone or chalk beds during the Phanerozoic eon.

Uses & applications

Used historically for stone tools and starting fires; currently used as a road aggregate, in jewelry (as jasper/agate), and by collectors.

Geological facts

Chert was one of the most important materials for early humans because its conchoidal fracture produces extremely sharp edges, ideal for arrowheads and scrapers.

Field identification & locations

Identify in the field by its hardness (scratches glass), waxy texture, and shell-like fracture pattern. Often found as nodules weathering out of limestone cliffs or in riverbeds.