sedimentary

Chert (Agatized Chert)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Grayish-yellow to translucent tan; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Grayish-yellow to translucent tan
Luster: Waxy to vitreous

Identified April 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains or by the precipitation of silica from groundwater within limestone or other sedimentary formations. This specimen appears to be an agatized or chalcedony-rich variety often found in ancient marine beds.

Uses & applications

Historically used for stone tools (knapping) due to its sharp conchoidal edges; currently used for lapidary work, jewelry, and as a decorative landscaping stone.

Geological facts

Chert was one of the most important minerals for early humans, used to create arrowheads, scrapers, and blades. Because it is harder than steel, it can produce sparks when struck against iron, making it useful for fire-starting.

Field identification & locations

Identify in the field by its waxy texture and shell-like (conchoidal) fractures. It will easily scratch glass and cannot be scratched by a steel knife. Commonly found in stream beds or weathering out of limestone cliffs.

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