sedimentary

Banded Chert

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale), Color: Brown and tan/cream banding, Luster: Waxy to vitreous (especially when wet), Crystal Structure: Cryptocrystalline, Cleavage: None (has conchoidal fracture), Specific Gravity: 2.6

Identified March 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from sea water in marine environments. The banding represents changes in mineral impurities or deposition rates over geological time, often dating from the Paleozoic to Mesozoic eras.

Uses & applications

Used historically for stone tools and arrowheads due to its sharp edges. Modern uses include road aggregate, landscape stone, and as a lapidary material for jewelry like cabochons and tumbled stones.

Geological facts

Chert is so hard it can strike sparks against steel, a property that led to its use in flintlock firearms. Banded varieties are often found as water-worn pebbles in riverbeds or beaches, having survived transport due to their high durability.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), its smooth waxy feel, and the way it breaks into curved 'shell-like' fragments (conchoidal fracture). Commonly found in limestone beds or as gravel in river deposits globally.