sedimentary

Chert (Jasper/Flint variety)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale), Color: tan, green, or brown banding (often called 'Wonderstone' or banded chert), Luster: waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Identified April 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of siliceous remains of organisms like diatoms or radiolarians, or through chemical precipitation in groundwater replacing limestone. This specimen shows distinct banding, likely from periodic deposition or mineral staining in a sedimentary environment.

Uses & applications

Historically used for making sharp tools and arrowheads. Currently used as an ornamental stone, for lapidary work (cabochons), and as a landscaping or construction aggregate.

Geological facts

Because of its conchoidal fracture, it breaks with very sharp edges, which is why it was the primary material for prehistoric survival tools globally. Bicolor or banded varieties are often nicknamed 'Wonderstone' if they originate from volcanic ash alteration.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its smooth, shell-like fracture pattern. It often has a waxy feel when freshly broken and can produce sparks when struck against steel.

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