sedimentary

Red Chert (Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Red to reddish-brown (from iron inclusions); Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline quartz; Cleavage: None (conchoidal fracture); Specific gravity: 2.6 - 2.7

Hardness: 6
Color: Red to reddish-brown (from iron inclusions)
Luster: Waxy to dull

Identified March 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation in marine environments. Often found in Precambrian and Paleozoic rock formations, frequently appearing as nodules or bedded layers.

Uses & applications

Used historically for stone tools and weapons due to its sharp conchoidal fracture. Modern uses include decorative gravel, lapidary work (jewelry, cabochons), and as a component in construction aggregate.

Geological facts

Red chert is often referred to as 'red jasper' when it is opaque and heavily colored by iron oxide (hematite). Because of its hardness and sharpness when broken, it was a primary material for arrowheads and scrapers among ancient civilizations.

Field identification & locations

Identify in the field by its characteristic shell-like (conchoidal) fracture pattern and its ability to scratch glass. It is commonly found in riverbeds, glacial tills, and coastal deposits across the United States, particularly in the Great Lakes region and the Southwest.