sedimentary

Chert (often found within Limestone)

Silicon Dioxide (SiO2) - Microcrystalline Quartz

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Structure: Cryptocrystalline (microscopic crystals); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 6
Color: Gray, tan, or brown
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, or brown; Luster: Waxy to dull; Structure: Cryptocrystalline (microscopic crystals); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed as nodules or layers in carbonate rocks through the precipitation of silica from groundwater or the accumulation of siliceous skeletal remains (like diatoms or sponges) on the seafloor.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; today used in construction aggregate and as a collector's specimen.

Geological facts

Chert is extremely durable and weather-resistant; it often survives long after the surrounding limestone host rock has eroded away. It produces sparks when struck against steel.

Field identification & locations

Identify by its waxy texture, extreme hardness (it will scratch glass), and smooth, curved (conchoidal) breaks. Often found in limestone outcrops or as rounded pebbles in riverbeds.