sedimentary

Chert (potentially Jasper/Common Opal mixture)

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Variable (browns, tans, purple-grey); Luster: Dull to waxy; Crystal Structure: Cryptocrystalline (non-visible); Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.7

Hardness: 6
Color: Variable (browns, tans, purple-grey)
Luster: Dull to waxy

Identified June 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms primarily through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids. Often found in seafloor deposits or as nodules in limestone/chalk.

Uses & applications

Historically used for stone tools (arrowheads). Currently used as an industrial abrasive, in road construction (aggregate), and as decorative landscaping stone. High-quality colorful pieces are used for lapidary work.

Geological facts

Because it breaks with a conchoidal fracture like glass, it creates extremely sharp edges; it was one of the most vital materials for prehistoric human survival.

Field identification & locations

Identify by its smooth, flint-like fracture and high hardness (it will scratch glass but cannot be scratched by a steel knife). Commonly found in sedimentary basins and riverbeds as rounded 'river rocks'.