sedimentary

Chert (specifically Jasper)

Silicon dioxide (SiO2) with iron oxide inclusions

Hardness: 6.5-7 (Mohs); Color: Mottled green, reddish-brown, and grey; Luster: Dull to waxy; Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.91

Hardness: 6
Color: Mottled green, reddish-brown, and grey
Luster: Dull to waxy

Identified March 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils or chemical precipitation from hydrothermal fluids in sedimentary environments. Can be found in geological formations spanning billions of years, often in nodules or bedded deposits.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges; modernly used for lapidary work, jewelry (cabochons), and landscaping stones.

Geological facts

Jasper is an opaque variety of chalcedony. Its colors are caused by impurities; the reddish tones in this specimen are likely due to hematite (iron oxide). It was one of the first materials used by early humans for tools because of its predictable fracture patterns.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), smooth waxy feel, and characteristic shell-like (conchoidal) fractures. Found globally, especially in riverbeds or marine sedimentary rock outcrops.

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