sedimentary

Chert (Jasper/Common Opal transition)

Microcrystalline Quartz (SiO2) with iron oxide inclusions

Hardness: 6.5-7 (Mohs scale), Color: Brownish-gold to mustard yellow, Luster: Waxy to dull, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Hardness: 6

Identified June 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (radiolaria or diatoms) or chemical precipitation in marine or volcanic environments. Often associated with the replacement of organic material or volcanic ash. Common in various geological ages ranging from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools due to its sharp edges when fractured. Today used for lapidary work, landscaping, as a collector's specimen, and occasionally for industrial abrasives.

Geological facts

This specimen shows significant iron oxide staining, giving it its earthy gold appearance. Chert is extremely durable and can survive long-distance transport in riverbeds. It was one of the first minerals used by early humans to create fire and weapons.

Field identification & locations

Identified by its waxy luster, conchoidal (shell-like) fracture, and high hardness (it will scratch glass). Often found in limestone beds or as nodules in volcanic soil. Look for smooth, curved break patterns on the edges.

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