sedimentary
Chert (Green Chert)
Microcrystalline silica (SiO2)
Hardness: 7 on Mohs scale; Color: olive green, tan, and brown mottled; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- olive green, tan, and brown mottled
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: olive green, tan, and brown mottled; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed via the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments; age varies from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools (arrowheads); currently used as river rock for landscaping, as an abrasive, and occasionally for lapidary work or semi-precious jewelry.
Geological facts
Chert is so hard it can strike sparks against steel. The green color is often caused by the presence of minerals like chlorite or celadonite within the silica matrix.
Field identification & locations
Identify in the field by its smooth, waxy texture when wet, high hardness (cannot be scratched by a steel knife), and characteristic curved (conchoidal) fractures. Common in riverbeds and limestone outcrops.
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