sedimentary

Chert (Jasper)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 (Mohs); Color: Dark brown to black; Luster: Waxy to dull (wet in photo); Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 6
Color: Dark brown to black
Luster: Waxy to dull (wet in photo)

Identified July 14, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Dark brown to black; Luster: Waxy to dull (wet in photo); Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine environments, followed by diagenesis and compaction over millions of years.

Uses & applications

Historically used for stone tools due to sharp edges; currently used for decorative gravel, landscaping, and lapidary work.

Geological facts

This specimen shows typical conchoidal fracturing and a dense, fine-grained texture. When dry, it likely has a waxy appearance. Chert can contain microscopic fossils of prehistoric sea creatures.

Field identification & locations

Identified by its high hardness (scratches glass) and smooth, shell-like fracture patterns. Often found as nodules in limestone or as water-worn cobbles in riverbeds and beaches.