sedimentary

Chert (Jasper)

Cryptocrystalline Silica (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: Variegated brown/white/grey, Luster: Waxy to vitreous when wet, Structure: Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7.

Hardness: 6

Identified June 30, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale), Color: Variegated brown/white/grey, Luster: Waxy to vitreous when wet, Structure: Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7.

Formation & geological history

Formed via the accumulation of silica-rich organic remains or chemical precipitation within sedimentary layers. This specific specimen appears to be a stream-tumbled pebble likely originating from Paleozoic or Mesozoic formations.

Uses & applications

Historically used for stone tools/arrowheads. Modern uses include decorative gravel, lapidary polishing, and as various forms of semi-precious gemstones (Jasper).

Geological facts

Chert has been used by humans for millions of years because its conchoidal fracture creates extremely sharp edges. It is one of the most common materials for prehistoric tool-making.

Field identification & locations

Identify by its high hardness (it will scratch glass) and smooth, waxy surface. Look for the characteristic jagged, curved 'shell-like' breaks if the stone is chipped. Commonly found in riverbeds or coastal deposits.