sedimentary

Chert (Quartz var.)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: Beige, tan, or reddish-brown with white bands/vessels, Luster: Waxy to vitreous, Crystal Structure: Cryptocrystalline quartz, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Identified June 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by the replacement of limestone with silica via groundwater. Common in sedimentary basins and often found as nodules or layers.

Uses & applications

Historically used for stone tools (flintknapping); currently used as a raw material for ceramics, construction aggregate, and as a semi-precious lapidary material for jewelry and cabochons.

Geological facts

Chert is so hard that it can strike sparks from steel. The user's note about it being difficult for a diamond blade suggests a very high silica content. The 'little diamonds' described are likely druzy quartz crystals that grew in small cavities or fractures within the specimen.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and waxy texture. Found frequently in the Trans-Mexican Volcanic Belt region where silica-rich geological activity is common. Small druzy quartz crystals inside are a common diagnostic feature.