sedimentary

Sandstone (Nut-stone / Cup-stone artifact)

Quartz Arenite / Worked Sedimentary Rock

Hardness: 6-7 (quartz grains), Color: reddish-orange due to iron oxide (hematite/limonite) staining, Luster: dull or earthy, Texture: clastic/granular with a distinct artificially or naturally pecked depression (cupule).

Identified August 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation, compaction, and cementation of mineral particles (primarily quartz sand) in ancient depositional environments such as deserts, rivers, or beaches, often subsequently stained by groundwater iron-rich solutions.

Uses & applications

Commonly used historically as native American or prehistoric grinding tools, nutting stones, anvil stones, or ceremonial cupstones. Also serves as building stone and abrasive material.

Geological facts

Stones featuring cup-like depressions are often studied by archaeologists and geologists alike. While some depressions form naturally via differential weathering or pot-holing, many were intentionally pecked and used by early humans to crack nuts, grind seeds, or start fires using the bow-drill method.

Field identification & locations

Look for sedimentary grain textures alongside unusual, symmetrical depressions or wear marks. Often found near historical habitation sites, riverbeds, or outcrops of weathered sandstone.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Quartz pebble

Silicon dioxide (SiO2)

sedimentary

Generic Pebble / Rock Fragment

Lithic fragment / Weathered rock

sedimentary

Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

fossil

Sedimentary Sandstone

Arenite (Sedimentary Rock)

sedimentary

Banded Siltstone / Mudstone Pebble

Siltstone / Argillite

sedimentary