sedimentary

Moqui Marble (Ironstone Concretion)

Goethite-limonite concretion (primarily FeO(OH) with Sandstone)

Hardness: 5-5.5 (outer shell); Color: Rusty brown, blackish, or tan; Luster: Dull to sub-metallic; Crystal Structure: Amorphous/microcrystalline shell over granular sand core; Cleavage: None; Specific Gravity: 3.3-4.3 (shell)

Hardness: 5-5
Color: Rusty brown, blackish, or tan
Luster: Dull to sub-metallic

Identified June 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Moqui Marbles are formed by the precipitation of iron oxide minerals around a nucleus (like a grain of sand) within the Navajo Sandstone. They formed during the Jurassic period, roughly 130 to 180 million years ago, through groundwater movement.

Uses & applications

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

Geological facts

They are often called 'Moqui Marbles' after the Hopi tribe (formerly known as Moqui). NASA scientists are interested in them because they are nearly identical to hematite concretions found on Mars by the Opportunity rover.

Field identification & locations

Identified by their distinct spherical or 'flying saucer' shapes, heavy weight for their size, and rough, sandy texture. Commonly found in the Navajo Sandstone of southern Utah. Collecting is strictly prohibited within National Park boundaries.

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