sedimentary

Green Chert

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: olive green; Luster: waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: none, exhibits conchoidal fracture; Specific gravity: 2.5-2.8

Hardness: 6
Color: olive green
Luster: waxy to dull

Identified July 19, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: olive green; Luster: waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: none, exhibits conchoidal fracture; Specific gravity: 2.5-2.8

Formation & geological history

Formed as a chemical precipitate or as a biochemical accumulation of silica-rich microfossils (like radiolaria or diatoms) in deep-sea environments. Often found in layered beds or as nodules within limestone or chalk.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges when fractured. Modern uses include lapidary work, decorative landscaping, and as an industrial abrasive.

Geological facts

Chert is so hard it can strike sparks against steel. The green color is often caused by the presence of chlorite, celadonite, or glauconite within the silica matrix.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) breakage patterns. Found globally in sedimentary basins, notably in the Coast Ranges of California or the English Chalk beds.