sedimentary
Ironstone Concretion (Moqui Marble type)
Ferruginous Concretion (Fe2O3 / FeO(OH))
Hardness: 5-6 (outer shell); Color: Brown, rusty red, or dark grey; Luster: Dull/Earthy; Crystal structure: Amorphous or microcrystalline (Limonite/Hematite); High specific gravity due to iron content; often features a central sandy core.
- Hardness
- 5-6 (outer shell)
- Color
- Brown, rusty red, or dark grey
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 (outer shell); Color: Brown, rusty red, or dark grey; Luster: Dull/Earthy; Crystal structure: Amorphous or microcrystalline (Limonite/Hematite); High specific gravity due to iron content; often features a central sandy core.
Formation & geological history
Formed by the precipitation of iron oxide minerals from groundwater within porous sedimentary rocks, typically sandstone. These minerals cement sand grains together into spherical shapes during the Diagenesis process over millions of years.
Uses & applications
Primarily of interest to geologists and collectors; used as decorative 'curiosity' stones; historically used by indigenous cultures for spiritual purposes or as paint pigment.
Geological facts
Also known as 'Moqui Marbles' or 'Shaman Stones.' Similar spherical hematite concretions, nicknamed 'blueberries,' were discovered on Mars by the Opportunity rover, suggesting the past presence of liquid water on the red planet.
Field identification & locations
Identify by its unusually perfect spherical or ellipsoidal shape and heavy weight relative to its size. Often found in eroded sandstone landscapes like Utah's Navajo Sandstone. Collectors look for the distinct 'seam' or ring often visible around the middle of the sphere.
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