sedimentary

Grooved Maun Ball (Maul/Hammerstone-like Concretion)

Calcareous/Ferruginous Concretion in Sandstone Matrix

AI-generated identification · may be incorrect

Hardness: 5-7 (Mohs); Color: Tan, brown, or reddish-brown; Luster: Dull/Earthy; Texture: Granular and clastic; Specific Gravity: Approx. 2.6 - 3.0. The specimen shows a distinct equatorial groove indicative of cultural modification or unique erosional weathering.

Hardness: 5-7 (Mohs)
Color: Tan, brown, or reddish-brown
Luster: Dull/Earthy

Identified January 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of mineral cement in the spaces between grains of sediment, typically around a nucleus. These range from millions of years old to relatively modern. The specific spherical shape and groove suggest either a Moqui Marble-type concretion or an anthropogenic stone tool formed from sphaeroidal sediment.

Uses & applications

Historically used as stone tools (mauls, club heads, or hammerstones) by indigenous populations. Geologically, these are prized as collector's specimens. In some cases, they are studied to understand paleo-groundwater flow.

Geological facts

Specimens like this are often found in the American Southwest and are sometimes referred to as 'Moqui Marbles' or 'Klerksdorp spheres' depending on the location and age. While many are natural, the precise encircling groove on this specimen is characteristic of 'grooved mauls' used for crushing and hammering.

Field identification & locations

Identify by its spherical symmetry and differential hardening compared to surrounding rock. Look for them in eroding sandstone cliffs or dry creek beds. If found with a distinct, deep groove, it may have archaeological significance as a tool rather than just a geological curiosity.

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