sedimentary

Chert (Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs; Color: Black, red, brown, and tan; Luster: Vitreous to waxy (when polished); Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 6
Color: Black, red, brown, and tan
Luster: Vitreous to waxy (when polished)

Identified May 31, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils or chemical precipitation in marine environments, often undergoing secondary mineralization that introduces iron oxides (red) and organic material (black).

Uses & applications

Used for making jewelry (cabochons), lapidary art, and historically for stone tools due to its sharp edges when broken.

Geological facts

Black and red jasper combinations are often aesthetically called 'Bloodstone' or 'Dragon Blood Jasper' depending on the pattern, though this specimen is a classic silicated creek or beach pebble.

Field identification & locations

Identify in the field by its hardness (cannot be scratched by a steel knife), smooth texture, and characteristic curved (conchoidal) fractures. Frequently found in riverbeds and glacial deposits.