sedimentary

Chert (Jasper variation)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

Hardness: 7 (Mohs scale), Color: Dark brown/black with yellow-brown (ochre) banding, Luster: Waxy to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Identified June 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms) or by the replacement of limestone. This specimen appears to have undergone secondary oxidation or staining, creating the yellow band. Geologically, it can range from Paleozoic to more recent ages.

Uses & applications

Historically used for stone tools due to its sharp conchoidal fracture. Modern uses include decorative lapidary work, jewelry (especially the jasper variety), and as a minor fluxing agent in metallurgical processes.

Geological facts

Chert comes in many varieties; when it is colorful and opaque, it is often called Jasper. It was one of the first minerals utilized by early humans to create arrowheads, knives, and scrapers because of its extreme toughness and sharp edges.

Field identification & locations

Identify in the field by its hardness (it will scratch glass easily), its smooth waxy surface, and characteristic curved (conchoidal) fractures. Commonly found in limestone beds or as stream pebbles.

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