sedimentary

Chert (with Quartz Vein)

Chert (Siliceous sedimentary rock, predominantly Microcrystalline Quartz SiO2)

Hardness: 7 on Mohs scale; Color: Dark grey to brown matrix with white mineral vein; Luster: Waxy to dull matrix, vitreous vein; Crystal structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Dark grey to brown matrix with white mineral vein
Luster: Waxy to dull matrix, vitreous vein

Identified April 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. The white vein formed later via hydrothermal activity or groundwater mineral deposition in rock fractures.

Uses & applications

Historically used as stone tools (arrowheads/scrapers) due to conchoidal fracture. Currently used as road aggregate, in landscaping, and as a polishing material in rock tumblers.

Geological facts

Chert is so hard it can actually scratch steel. When struck against steel, it can create sparks, a property shared with its variety, flint. The white band visible is a secondary quartz vein that filled a crack in the older host rock.

Field identification & locations

Identify in the field by its hardness (will scratch glass), smooth waxy texture on fresh breaks, and distinct conchoidal (shell-like) fracture patterns. Found globally in limestone formations.

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