sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Light gray, white, tan, or brown; Luster: Waxy to vitreous; Crystal structure: Microcrystalline/cryptocrystalline quartz (chalcedony); Cleavage: None, exhibits conchoidal fracture; Specific gravity: 2.60 - 2.65

Hardness: 7 on Mohs scale
Color: Light gray, white, tan, or brown
Luster: Waxy to vitreous

Identified August 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical precipitation of silica from aqueous solutions, often derived from the skeletal remains of marine microorganisms (like diatoms or radiolarians) accumulating in deep-marine environments or via the replacement of limestone.

Uses & applications

Historically used by early humans for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Today used occasionally in abrasives or decorative landscaping.

Geological facts

Chert breaks with extremely sharp edges, making it one of the premier materials for prehistoric tool-making across the globe. Varieties of chert include flint and jasper.

Field identification & locations

Easily identified in the field by its smooth, waxy luster, conchoidal fracture patterns, and hardness that easily scratches glass. Commonly found within limestone or chalk formations worldwide.