sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

Hardness: 7 Mohs scale; Color: Tan, beige, creamy white; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 Mohs scale
Color: Tan, beige, creamy white
Luster: Dull to waxy

Identified July 9, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Tan, beige, creamy white; Luster: Dull to waxy; Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed in marine environments through the precipitation of silica or the accumulation of siliceous remains such as diatoms or radiolarians. It often occurs as nodules or layers within limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges when broken. Today used as road base, decorative landscaping stone, and occasionally in jewelry as jasper or agate variants.

Geological facts

Because it is extremely hard and resistant to weathering, chert often remains as gravel in stream beds long after the surrounding limestone has eroded away. It is one of the oldest materials used by early humans for technology.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its signature conchoidal (shell-like) fracture patterns. It often has a waxy feel on freshly broken surfaces. Found globally in sedimentary basins.