sedimentary

Chert (Chert Pebble)

Microcrystalline or cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish; Luster: Waxy to dull; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Tan, brown, or grayish
Luster: Waxy to dull

Identified March 9, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Tan, brown, or grayish; Luster: Waxy to dull; Crystal structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from silica-rich groundwater within limestone or chalk beds. Often smooth and rounded due to water erosion (river or beach tumbling).

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges; modernly used in road construction, as an abrasive, and small polished specimens for hobbyist collecting.

Geological facts

Chert is so hard it can scratch glass and steel. Because it breaks with a conchoidal (shell-like) fracture, it was one of the most important minerals for early human survival for making fire and weapons.

Field identification & locations

Identify in the field by its hardness (will scratch a knife blade) and its smooth, waxy feel. Commonly found in riverbeds, glacial till, and as nodules within sedimentary rock outcrops globally.