sedimentary

Pitted Sedimentary Rock / Cupstone

Sedimentary rock with weathering pit (arenite / sandstone)

Hardness varies around 6-7 on Mohs scale depending on cementation; brown to reddish-brown color; dull or earthy luster; clastic crystal structure; lacks distinct cleavage; specific gravity around 2.2-2.6.

Identified August 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation, compaction, and cementation of mineral particles or rock fragments over millions of years, often in riverbeds or marine environments, with subsequent localized weathering or human modification creating the depression.

Uses & applications

Often collected as a geological curiosity, natural artifact, or potential prehistoric tool (such as a nutting stone or cupstone).

Geological facts

Naturally formed circular depressions in rocks can be created by pebbles swirling in fast-flowing water (potholes), differential weathering of softer inclusions, or they can be Native American artifacts known as cupstones or anvil stones used for cracking nuts or grinding pigments.

Field identification & locations

Found along riverbanks, beaches, and in sedimentary rock formations. Collectors look for unique weathering patterns and symmetrical depressions.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Fossiliferous Concretion

Septarian Concretion containing Brachiopods/Crinoids

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Quartz pebble

Silicon dioxide (SiO2)

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Sedimentary Sandstone

Arenite (Sedimentary Rock)

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Generic Pebble / Rock Fragment

Lithic fragment / Weathered rock

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Banded Siltstone / Mudstone Pebble

Siltstone / Argillite

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