sedimentary

Yellow Chert (Microcrystalline Quartz)

Chert / SiO2 (Silicon Dioxide)

Hardness: 7 (Mohs scale); Color: Yellow to tan with brown impurities; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Yellow to tan with brown impurities
Luster: Waxy to dull

Identified March 15, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine or groundwater environments. This specimen appears water-worn, likely from a stream or alluvial deposit.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to its sharp edges; modernly used as road aggregate, architectural stone, or tumbled for landscaping and decorative gravel.

Geological facts

Chert is so durable that it often survives millions of years of erosion that destroy surrounding rocks. It has been used by humans since the Stone Age because it breaks with incredibly sharp, glass-like edges.

Field identification & locations

Identify in the field by its hardness (will scratch glass and steel) and its distinctive conchoidal (curved, shell-like) fracture. Commonly found in riverbeds, gravel pits, and as nodules in limestone.

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