sedimentary

Chert (Yellow Jasper)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Yellowish-brown (due to iron oxides); Luster: Dull to waxy; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Yellowish-brown (due to iron oxides)
Luster: Dull to waxy

Identified January 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or inorganic precipitation from silica-rich fluids. It occurs as nodules or bedded deposits within limestone or dolomite. Geological age varies from Precambrian to modern.

Uses & applications

Historically used for stone tools/weaponry (arrowheads) due to sharp edges; currently used in lapidary work, jewelry (cabochons), landscaping, and as an abrasive in some industrial processes.

Geological facts

Jasper is an opaque variety of chert. The yellow coloring is specifically known as 'Yellow Jasper' or 'Mookite' depending on the locality. It has been used by humans for over a million years for tool-making.

Field identification & locations

Identify in the field by its characteristic smooth, shell-like (conchoidal) fracture and its ability to scratch glass. It is commonly found in stream beds, gravel pits, and within sedimentary rock outcrops globally. Collectors should look for its smooth texture compared to surrounding rocks.