sedimentary

Chert (Jasper/Flint variation)

Chert (SiO2)

Hardness: 6.5-7 (Mohs); Color: Mottled grey, green, and brown; Luster: Dull to waxy; Crystal Structure: Microcrystalline (Trigonal); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Mottled grey, green, and brown
Luster: Dull to waxy

Identified May 6, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Mottled grey, green, and brown; Luster: Dull to waxy; Crystal Structure: Microcrystalline (Trigonal); Cleavage: None (Conchoidal fracture); Specific Gravity: 2.6-2.7

Formation & geological history

Formed from the accumulation of silica-rich microfossils like diatoms or radiolarians, or through chemical precipitation in marine environments. Often found as nodules within limestone or chalk beds.

Uses & applications

Historically used for stone tools and fire-striking. Today used in construction aggregate, as landscaping stone, and as tumbled gemstones for collectors.

Geological facts

Chert is a cryptocrystalline variety of quartz. Its conchoidal fracture pattern creates sharp edges, which is why it was the primary material for prehistoric arrowheads and spear points.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its smooth, shell-like fracture surfaces. Often found in riverbeds or coastal areas where softer surrounding rock has eroded away.