sedimentary

Ironstone Concretion (Moqui Marble)

Iron Oxide Concretion (Fe2O3 / FeO(OH) mixed with SiO2)

AI-generated identification · may be incorrect

Hardness: 5-6 (outer shell); Color: Dark brown, rusty red, or black; Luster: Dull to earthy; Crystal structure: Amorphous or microcrystalline; Cleavage: None; Specific Gravity: 3.4-4.2

Hardness: 5-6 (outer shell)
Color: Dark brown, rusty red, or black
Luster: Dull to earthy

Identified May 7, 2026More sedimentary →

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Physical properties

Hardness: 5-6 (outer shell); Color: Dark brown, rusty red, or black; Luster: Dull to earthy; Crystal structure: Amorphous or microcrystalline; Cleavage: None; Specific Gravity: 3.4-4.2

Formation & geological history

Formed when iron-rich minerals precipitate from flowing groundwater within porous sedimentary rock (usually sandstone). They often form around a nucleus. They range from Jurassic to modern geological ages.

Uses & applications

Primarily used for geological study, educational specimens, and novelty collecting. Some spiritual practices use them as balancing stones.

Geological facts

Similar concretions have been discovered on Mars by the Opportunity rover, where they are nicknamed 'blueberries,' suggesting water once flowed on the Martian surface.

Field identification & locations

Identify by a hard, dark, iron-rich outer shell often surrounding a softer sandstone core. They are common in the Navajo Sandstone of Utah and Arizona. Look for spherical or 'pothole' shapes in desert washes.