sedimentary

Moqui Marble (Ironstone Concretion)

Goethite/Hematite Concretion (Fe2O3 / FeO(OH))

Hardness: 5-5.5 (outer shell), 3-4 (inner core). Color: Dark brown, rusty orange, or tan. Luster: Dull/Earthy to sub-metallic. Crystal structure: Amorphous or microcrystalline shell around a sandstone center.

Hardness: 5-5
Color: Dark brown, rusty orange, or tan
Luster: Dull/Earthy to sub-metallic

Identified March 22, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed during the Jurassic period (approx. 190 million years ago) via groundwater precipitation. Iron minerals dissolved in water precipitated around a nucleus within porous sandstone, eventually forming a hardened shell.

Uses & applications

Primarily collected as geological curiosities, used in metaphysical practices ('shaman stones'), and studied by NASA as terrestrial analogs to 'blueberries' found on Mars.

Geological facts

They are named after the Hopi Tribe (formerly 'Moqui'). On Mars, the Opportunity rover found near-identical structures composed of hematite, suggesting that liquid water once existed on the Red Planet.

Field identification & locations

Identified by their round/ellipsoidal shape, heavy weight for their size, and distinct dark iron-rich crust. Found primarily in the Navajo Sandstone of Utah and Arizona. Collectors should look for weathered outcrops.

Other sedimentary specimens

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Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sandstone

Arenite (primarily SiO2)

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Shale or Slaty Mudstone

Argillaceous sedimentary rock

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Chert Breccia

Brecciated Chert (Microcrystalline Silica)

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Sandstone (Quartz-rich)

Arenite (SiO2)

sedimentary

Sandstone (with man-made markings)

Arenite (composed primarily of Quartz, SiO2)

sedimentary