sedimentary

Chert (Jasper)

Jasper (Silicon Dioxide, SiO2)

Hardness: 6.5-7.0 (Mohs); Color: Dark reddish-brown to maroon; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.91

Hardness: 6
Color: Dark reddish-brown to maroon
Luster: Dull to waxy

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7.0 (Mohs); Color: Dark reddish-brown to maroon; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.91

Formation & geological history

Formed through the accumulation of silica-rich microfossils or precipitation from hydrothermal fluids in sedimentary basins. The red color is typically due to iron (hematite) inclusions.

Uses & applications

Historically used for stone tools due to its sharp conchoidal fracture. Today used for lapidary work, cabochons, and as a collector's specimen.

Geological facts

Red jasper was frequently used in the ancient world for seals and amulets. It is unique among quartz varieties because of its high opacity and fine-grained texture.

Field identification & locations

Look for a smooth, waxy surface with shell-like (conchoidal) fractures and high hardness (it will scratch glass). Commonly found in riverbeds or within limestone and dolomite formations.