sedimentary

Chert

Chert (SiO2)

Hardness: 7 on Mohs scale; Color: Cream, white, or light tan; Luster: Waxy to dull; Crystal Structure: Microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Cream, white, or light tan
Luster: Waxy to dull

Identified June 30, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Cream, white, or light tan; Luster: Waxy to dull; Crystal Structure: Microcrystalline quartz; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed in marine environments through the precipitation of silica from seawater or from the accumulation of siliceous organisms like radiolaria or diatoms. It can also form as nodules in limestone beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges when broken. Today used as road aggregate, in laboratory equipment, and as a low-cost lapidary material.

Geological facts

Chert is essentially the same material as flint, but the term 'flint' is often reserved for dark gray or black chert found specifically in chalk deposits. It is extremely durable and chemically stable.

Field identification & locations

Identified in the field by its hardness (will scratch glass), fine-grained texture, and characteristic curved, shell-like (conchoidal) fractures. Found globally in sedimentary rock outcrops.