sedimentary

Chert (Jasper)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 (can scratch glass). Color: Yellowish-brown, tan, and reddish hues. Luster: Waxy to dull. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.7.

Hardness: 6
Color: Yellowish-brown, tan, and reddish hues
Luster: Waxy to dull

Identified June 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from silica-saturated fluids in limestone or chalk beds. Often found in central Texas as nodules within Cretaceous sedimentary layers.

Uses & applications

Historically used for making stone tools (arrowheads). Today used locally for landscaping, as a decorative lapidary material, or as aggregate in construction.

Geological facts

This specimen is likely a water-worn river cobble. Chert is extremely durable and chemical-resistant, allowing it to survive long-distance transport in river systems long after the softer surrounding limestone has eroded.

Field identification & locations

Common in central/east Texas. Identify by its smooth, waxy surface and conchoidal (shell-like) fractures where it has been chipped. The coordinates provided (Limestone County) are highly consistent with findspots for silica-rich gravels and nodules.