sedimentary

Chert (Jasper/Flint variety)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Brown, tan, and reddish hues due to iron inclusions; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Brown, tan, and reddish hues due to iron inclusions
Luster: Waxy to dull

Identified April 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by the chemical replacement of limestone/dolomite. This specimen appears to be a weathered nodule or fragment from a larger bedded formation.

Uses & applications

Historically used for tool making (arrowheads, scrapers) due to conchoidal fracture. Modern uses include road surfacing, landscaping, and lapidary work for jewelry if colorful enough (Jasper).

Geological facts

Chert was one of the most important minerals for early humans. It sparks when struck against steel, making it vital for early firearms (flintlocks) and fire starting.

Field identification & locations

Identify in the field by its hardness (it will scratch glass and steel), its smooth waxy feel when freshly broken, and the lack of visible crystals. Commonly found in riverbeds or within limestone outcrops.

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