sedimentary

Chert (containing Quartz veins)

Chert (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, white; Luster: Waxy to dull; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 6
Color: Gray, tan, white
Luster: Waxy to dull

Identified June 1, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Gray, tan, white; Luster: Waxy to dull; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments. This specimen shows secondary quartz vein infilling through fractures.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to conchoidal fracture. Modern uses include road surfacing, decorative gravel, and jewelry when colorful (Jasper/Agate variations).

Geological facts

Chert is so hard it can strike sparks from steel, a property used by ancient people to start fires. It is chemically identical to quartz but has a much finer grain structure.

Field identification & locations

Identify by its waxy luster, hardness (it will scratch glass), and smooth, curved (conchoidal) breaks. Often found in limestone or chalk beds as nodules or layers.