sedimentary

Moqui Marble (Concretion)

Iron Oxide Concretion (Hematite-cemented Sandstone)

AI-generated identification · may be incorrect

Hardness: 5-6 (outer shell), color: tan to dark chocolate brown, luster: dull/earthy, crystal structure: amorphous to microcrystalline, cleavage: none, specific gravity: 3-5

Identified March 21, 2026More sedimentary →

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Physical properties

Hardness: 5-6 (outer shell), color: tan to dark chocolate brown, luster: dull/earthy, crystal structure: amorphous to microcrystalline, cleavage: none, specific gravity: 3-5

Formation & geological history

Formed via chemical precipitation of iron-rich minerals (hematite or goethite) within pore spaces of sandstone, often around a small nucleus like a fossil or pebble. Most famous examples come from the Jurassic-aged Navajo Sandstone (approx. 180-190 million years old).

Uses & applications

Used primarily as decorative collector specimens, metaphysical 'shaman stones,' and in geological education to study groundwater flow in sedimentary basins.

Geological facts

Also known as Navajo Cherries or Shaman Stones; very similar spherical concretions were discovered on Mars by the Opportunity rover, where they are nicknamed 'Martian Blueberries.'

Field identification & locations

Identified by its spherical or disc-like shape, sandy interior, and hard metallic outer shell; commonly found in the American Southwest (Utah/Arizona) and various beach deposits where wave action erodes them from surrounding sandstone cliffs.