sedimentary

Chert (Yellow/Tan Variety)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 6.5–7 on Mohs scale. Color: Tan, yellow-brown, or buff-colored. Luster: Dull to waxy. Crystal structure: Cryptocrystalline (hexagonal system). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Hardness: 6
Color: Tan, yellow-brown, or buff-colored
Luster: Dull to waxy

Identified March 24, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from seawater or groundwater. It typically occurs as nodules or layers in limestone or chalk beds. This specimen likely underwent significant mechanical weathering in a fluvial (river) or glacial environment to achieve its rounded, pebble-like shape.

Uses & applications

Used historically for stone tools and fire-starting. Today, it is used as road aggregate, in landscaping, and occasionally tumbled for jewelry or decorative stone collections.

Geological facts

Chert has a conchoidal fracture, allowing it to break into very sharp edges, which is why prehistoric humans used it for arrowheads and scrapers. Its yellow/brown color is usually due to trace amounts of iron oxide (limonite).

Field identification & locations

Identify in the field by its smooth, waxy feel and the way it can scratch glass. It often features a white 'rind' or weathering crust. Common in riverbeds and gravel pits worldwide. Collectors look for unique patterns or colors within the stone.

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