sedimentary/metamorphic

Quartzite Chert Pebble

Microcrystalline Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Yellowish-brown, tan, and grey with possible iron inclusion; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).

Hardness: 7 (Mohs scale)
Color: Yellowish-brown, tan, and grey with possible iron inclusion
Luster: Waxy to dull

Identified June 14, 2026More sedimentary/metamorphic →

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Physical properties

Hardness: 7 (Mohs scale); Color: Yellowish-brown, tan, and grey with possible iron inclusion; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture).

Formation & geological history

Formed primarily from the accumulation of microcrystalline silica on the seafloor or through the metamorphosis of quartz-rich sandstone. This specimen shows significant rounding due to water erosion, likely being a river or beach pebble from the Quaternary period.

Uses & applications

Used as aggregate in construction, as a lapidary material for tumbling, and historically as a source for stone tools/flintknapping.

Geological facts

This pebble shows traces of iron oxide staining which gives it the yellowish tint. Cherts and quartzites are among the most durable rocks and can survive hundreds of miles of transport by rivers.

Field identification & locations

Identify by its inability to be scratched by a steel knife and its smooth, water-worn texture. Commonly found in riverbeds, glacial tills, and along coastal beaches worldwide.

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