sedimentary
Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: Yellow-brown/tan, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Fracture: Conchoidal, Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: Yellow-brown/tan, Luster: Waxy to dull, Crystal structure: Cryptocrystalline, Fracture: Conchoidal, Specific gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains or through the chemical precipitation of silica in groundwater within sedimentary beds. Common in limestone and dolostone.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges; used in construction aggregate and as decorative landscaping stones.
Geological facts
This specimen shows a rhomboid or diamond shape, likely caused by natural fracture patterns or cleavage within the host rock where it formed as a nodule. Chert has been used by humans for over two million years.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its shell-like (conchoidal) fracture, and its waxy appearance. Commonly found in riverbeds or within limestone outcrops.
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