sedimentary

Chert / Jasper

Cryptocrystalline Quartz (SiO2)

Hardness (7 on Mohs scale), color can vary from tan, white, to deep red/maroon. It has a dull to waxy luster and a conchoidal fracture pattern.

Identified July 16, 2026More sedimentary →

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Physical properties

Hardness (7 on Mohs scale), color can vary from tan, white, to deep red/maroon. It has a dull to waxy luster and a conchoidal fracture pattern.

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or by chemical precipitation from hydrothermal fluids in sedimentary basins. Most common in ancient marine layers.

Uses & applications

Historically used for stone tools (arrowheads). Today used as decorative landscaping rock, in gravel mixes, and occasionally for cabochon jewelry if the color is vibrant.

Geological facts

Chert was one of the first materials used by early humans for tools because it breaks with sharp, glass-like edges. When it is red due to iron inclusions, it is often called Jasper.

Field identification & locations

Identify it by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like breaking pattern. It is commonly found as nodules within limestone or as pebbles in riverbeds.