sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Gray, tan, or white; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 6
Color: Gray, tan, or white
Luster: Waxy to dull

Identified June 13, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Gray, tan, or white; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in limestone or chalk beds. Commonly found in Paleozoic and Mesozoic sedimentary formations.

Uses & applications

Historically used for stone tools and arrowheads; currently used as construction aggregate, road base, and occasionally as a gemstone (jasper/agate varieties).

Geological facts

Chert is so hard it can produce sparks when struck against steel. Prehistoric humans highly valued it because it breaks with sharp, razor-like edges.

Field identification & locations

Identified by its conchoidal (shell-like) fracture, extreme hardness (scratches glass), and waxy texture. Commonly found as nodules in limestone outcrops or as pebbles in stream beds.