sedimentary

Chert (Jasper)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, mustard yellow, and olive green; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).

Hardness: 6
Color: Reddish-brown, mustard yellow, and olive green
Luster: Waxy to vitreous

Identified June 24, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown, mustard yellow, and olive green; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).

Formation & geological history

Formed from the accumulation of silica-rich micro-organisms (like radiolaria or diatoms) or from chemical precipitation in groundwater that replaces original organic material or sedimentary structures. Common in Paleozoic to Mesozoic strata.

Uses & applications

Historically used for stone tools (arrowheads); currently used as an ornamental gemstone, for lapidary work (cabochons), and in some aquarium landscaping.

Geological facts

Iron oxide inclusions are responsible for the rich red and yellow colors. Because of its hardness and toughness, it was a primary material for prehistoric 'flapping' or knapping.

Field identification & locations

Identify by its smooth, shell-like (conchoidal) fracture and its ability to scratch glass. Commonly found in riverbeds, glacial tills, or embedded within limestone and dolomite formations.