sedimentary

Chert (Quartz Variety)

Microcrystalline / Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Brownish-gray with white mottling; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 6
Color: Brownish-gray with white mottling
Luster: Waxy to dull

Identified May 31, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Brownish-gray with white mottling; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from groundwater within sedimentary beds. This waterworn specimen likely weathered out of limestone or chalk.

Uses & applications

Historically used for stone tools (knapping) and fire-starting. Today used as decorative gravel, in construction aggregate, and for river stone landscaping.

Geological facts

Chert is so durable that it often survives long after the surrounding rock has eroded away. Flint is a high-quality, dark variety of chert used historically for weaponry.

Field identification & locations

Identify by its 'waxy' texture, extreme hardness (it will scratch glass), and conchoidal (shell-like) fracture patterns. Frequently found in riverbeds and glacial tills.