sedimentary

Chert / Jasper

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 (Mohs), Color: Brownish-red to tan, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.58-2.91

Hardness: 6

Identified May 10, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs), Color: Brownish-red to tan, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Fracture: Conchoidal, Specific Gravity: 2.58-2.91

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the precipitation of silica in groundwater within sedimentary host rocks. Common in marine deposits.

Uses & applications

Used historically for stone tools due to its sharp conchoidal fracture. Modernly used in landscaping, as a gemstone (jasper), and for tumbling in lapidary.

Geological facts

Chert was one of the first minerals used by early humans for technology, specifically for making arrowheads and scrapers. Red varieties are typically called Jasper due to iron oxide impurities.

Field identification & locations

Identify by its hardness (scratches glass), waxy luster when broken, and curved (conchoidal) fracture surfaces. Commonly found in stream beds and coastal gravels.