sedimentary

Ironstone Concretion (Moqui Marble)

Ferruginous Concretion (Fe2O3 / FeO(OH))

AI-generated identification · may be incorrect

Hardness: 5-5.5 on Mohs scale; Color: Dark brown, reddish-brown, or tan; Luster: Dull/Earthy; Crystal structure: Amorphous or Microcrystalline; Specific Gravity: Approx 3.0-4.0

Hardness: 5-5
Color: Dark brown, reddish-brown, or tan
Luster: Dull/Earthy

Identified June 25, 2026More sedimentary →

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Physical properties

Hardness: 5-5.5 on Mohs scale; Color: Dark brown, reddish-brown, or tan; Luster: Dull/Earthy; Crystal structure: Amorphous or Microcrystalline; Specific Gravity: Approx 3.0-4.0

Formation & geological history

Formed through the precipitation of iron oxide minerals from groundwater within sandstone or shale beds, often around a central nucleus such as a fossil or pebble. Most common in Mesozoic formations like the Navajo Sandstone.

Uses & applications

Used primarily as decorative specimens for collectors, metaphysical 'shaman stones', and occasionally crushed for iron ore or as pigment.

Geological facts

These are often called 'Moqui Marbles' in Southwestern United States; they can range from the size of a pea to several meters across. They have an iron-rich outer shell and often a softer sandstone core.

Field identification & locations

Identify by its spherical or ellipsoidal shape, heavy weight for its size, and rusty/dark appearance; found frequently in arid desert environments where errosion exposes them in sandstone layers.