sedimentary

Chert (often called Flint or Jasper)

Microcrystalline or cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5–7 (Mohs scale); Color: Brown, tan, cream, and grey; Luster: Waxy to dull; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7

Hardness: 6
Color: Brown, tan, cream, and grey
Luster: Waxy to dull

Identified March 31, 2026More sedimentary →

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Physical properties

Hardness: 6.5–7 (Mohs scale); Color: Brown, tan, cream, and grey; Luster: Waxy to dull; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6–2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation from groundwater within sedimentary rock layers, often limestone or chalk. Can range from Precambrian to recent ages.

Uses & applications

Historically used for stone tools and weapons due to sharp conchoidal edges; currently used for landscaping, road ballast, lapidary art, and fire-striking kits.

Geological facts

Chert is so durable it survives for millions of years as river gravel long after the limestone it formed in has eroded away. 'Flint' is technically a dark grey to black variety of chert often found in chalk.

Field identification & locations

Identify in the field by its waxy texture, smooth conchoidal (shell-like) fractures when broken, and extreme hardness—it will easily scratch glass and even some steel.