sedimentary

Ironstone Concretion (Moqui Marble / Boji Stone)

Sedimentary Iron Oxide Concretion (Fe2O3 / FeO(OH))

AI-generated identification · may be incorrect

Hardness: 5.0-6.0 Mohs. Color: reddish-brown, dark brown, to iron-gray. Luster: earthy to metallic. Crystal structure: amorphous or microcrystalline hematite/goethite matrix around a sandstone interior. Specific gravity: 3.0-4.5.

Hardness: 5
Color: reddish-brown, dark brown, to iron-gray
Luster: earthy to metallic

Identified July 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in sedimentary rock formations, particularly sandstones, through the precipitation of iron mineral oxides dissolved in circulating groundwater around a organic nucleus or mineral core. Common in Mesozoic-aged sandstone beds.

Uses & applications

Used in novelty rock collecting, metaphysical practices, educational sets, and decorative specimens.

Geological facts

Ironstone concretions often form rounded, spherical, or irregular nodules. In Utah's Navajo Sandstone formation, smooth spherical iron concretions are locally known as 'Moqui Marbles'. Similar structures found on Mars by NASA's Opportunity rover were nicknamed 'blueberries'.

Field identification & locations

Identified by its distinctly heavy feel for its size, rounded/nodular form, magnetic attraction (sometimes weak), and dark reddish-brown earthy coating. Found in sedimentary basins worldwide, especially in arid sandstone regions like Utah and Arizona.