sedimentary

Yellow Chert Pebble

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale. Color: Mustard yellow, tan, orange-brown with white weathering cortex or inner layer. Luster: Waxy to dull. Crystal structure: Cryptocrystalline/Microcrystalline. Cleavage: None (conchoidal fracture). Specific gravity: ~2.65.

Hardness: 7 on Mohs scale
Luster: Waxy to dull

Identified July 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica-rich solutions within sedimentary rock layers (such as limestone or chalk) or from the accumulation of siliceous organism remains. Smooth, rounded shape indicates tumbling and weathering in a riverbed or coastal beach environment.

Uses & applications

Historically used for stone tools and flintknapping due to its sharp conchoidal fracture. Modern uses include tumbling, decorative gravel, landscaping, and lapidary work.

Geological facts

Chert colored yellow or reddish-brown by iron oxides is often called jasper or yellow jasper. Its extreme hardness allows it to scratch glass and steel easily.

Field identification & locations

Identify in the field by its waxy luster, smooth water-worn surface, high hardness (scratches glass), and distinct shell-like conchoidal fractures where chipped. Commonly found in riverbeds, gravel deposits, and sedimentary formations worldwide.

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