sedimentary

Chert (and Jasper pebble)

Microcrystalline Silica (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Gray-blue to olive green; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 – 2.7.

Hardness: 7 (Mohs scale)
Color: Gray-blue to olive green
Luster: Waxy to dull

Identified March 29, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Gray-blue to olive green; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6 – 2.7.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in marine environments. These specimens appear to be river-worn or beach-tumbled pebbles.

Uses & applications

Used historically for stone tools and weapons (flint knapping); currently used in road construction as gravel, for jewelry (when colorful/polished), and as abrasive material.

Geological facts

Chert is so hard it can create sparks when struck against steel. Prehistoric civilizations traded specific types of high-quality chert over hundreds of miles to make arrowheads and knives.

Field identification & locations

Identify by its 'shell-like' conchoidal fracture patterns and inability to be scratched by a steel pocket knife. Commonly found in stream beds, glacial till, and embedded in limestone layers.