sedimentary

Chert (Pebble)

Microcrystalline silica (SiO2)

Hardness: 7 (Mohs scale); Color: Brown, tan, and dark grey; Luster: Waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Brown, tan, and dark grey
Luster: Waxy to dull

Identified May 3, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Brown, tan, and dark grey; Luster: Waxy to dull; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation from groundwater within sedimentary layers. This water-worn pebble likely originated from ancient seabed deposits.

Uses & applications

Historically used for making stone tools (arrowheads). Today used in road construction, as decorative landscaping stone, and occasionally in lapidary work for jewelry components.

Geological facts

Chert is a very hard and durable rock that can produce sparks when struck against steel. It is nearly identical in composition to flint, though 'flint' usually refers to chert found in chalk or marly limestone.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel nail), smooth waxy texture, and conchoidal (shell-like) fracture patterns. Frequently found in riverbeds, glacial tills, and coastal beaches.