sedimentary

Chert (Jasper)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: reddish-brown (from iron oxides); Luster: dull to waxy; Structure: cryptocrystalline; Cleavage: none (conchoidal fracture).

Hardness: 6
Color: reddish-brown (from iron oxides)
Luster: dull to waxy

Identified July 4, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: reddish-brown (from iron oxides); Luster: dull to waxy; Structure: cryptocrystalline; Cleavage: none (conchoidal fracture).

Formation & geological history

Formed from the accumulation of silica-rich microfossils or chemical precipitation in sedimentary basins. The reddish hue indicates iron oxide staining, common in desert environments.

Uses & applications

Historically used for stone tools (knapping); currently used for decorative purposes, landscape gravel, and as a collector's specimen.

Geological facts

Chert is so durable that it often remains as 'desert pavement' long after surrounding softer rocks have eroded away. Red varieties are commonly called Jasper.

Field identification & locations

Identified by its extreme hardness (scratches glass) and smooth, waxy feel. Highly common in the Franklin Mountains and desert flats near El Paso, Texas (31.7°N, 106.4°W).