sedimentary

Chert (Jasper)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Cream, tan, and brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 6
Color: Cream, tan, and brown
Luster: Waxy to dull

Identified June 20, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Cream, tan, and brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation in marine or groundwater environments. Often found as nodules in limestone or as water-worn pebbles in riverbeds.

Uses & applications

Used historically for stone tools due to its sharp fracture edges. Modern uses include decorative gravel, lapidary work (polishing), and as a gemstone (Jasper) in jewelry.

Geological facts

Chert is so durable that it often survives millions of years of erosion, eventually washing up as smooth 'river rocks' long after the surrounding limestone has dissolved away.

Field identification & locations

Identify by its waxy texture, extreme hardness (it will scratch glass), and its tendency to break with smooth, curved surfaces (conchoidal fracture). Common in glacial till and riverbeds.