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Iron Oxide Concretion

Iron oxide concretions are a type of sedimentary rock formation that are created by the interaction of iron minerals and groundwater in porous rocks. They can be found on Earth and Mars.

Colors They Come In -

Dark brown to orange: Found in the Tibooburra-Milparinka region of New South Wales 
Red: The color of hematite, an iron oxide that is named after the Greek word for blood 
Yellow ochre: A dull yellow color that is a hydrate of iron oxide red 
Warm red: A color that is a hydrate of iron oxide red

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Fracture - Cube like

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Shape -

Spherical: Iron oxide concretions can be spherical or flattened spheres. 
Multi-sided: Iron oxide concretions can be 3 to 6 sided bodies that form in a single flat bed. 
Ellipsoidal: Iron oxide concretions can be ellipsoidal in shape. 
Elongated: Iron oxide concretions can be elongated in shape. 
Cylindrical: Iron oxide concretions can be cylindrical in shape. 
Irregular: Iron oxide concretions can be irregular in shape. 
Ovoid: Iron oxide concretions can be ovoid in shape. 
Spindle: Iron oxide concretions can be spindle in shape. 
Platter-shaped: Iron oxide concretions can be platter-shaped masses. 
Indented: Iron oxide concretions can be indented, with deeply infolded rinds.

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Luster - Shiny to Dull

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Texture - Botryoidal

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Streak - Red To Brown

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Locality -

Navajo Sandstone, Utah: These dark spheres are found in the red and white outcrops of Navajo Sandstone in the Southwestern United States. The concretions are made of a sandstone core surrounded by a hard iron-rich rind. 
Djadokhta Formation, Mongolia: These concretions are found in the Cretaceous Djadokhta Formation in the Gobi Desert. 
Tibooburra and Milparinka: These areas have small to large areas of ground littered with dark brown iron oxide fragments. 
Fort Massac State Park: Iron oxide concretions can be found at Fort Massac State Park. 

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Where They Can Be Found - Iron oxide concretions can be found in the Jurassic Navajo Sandstone of southern Utah. These structures are considered terrestrial analogs for concretions imaged on Mars. The Navajo concretions can be spheroidal, pipelike, or tabular with multicompartmented boxworks.

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Hardness On The Mohs Scale -

Hematite: Has a hardness of 5.5 to 6.5 out of 10 on the Mohs scale.
Magnetite: Has a hardness of 5 to 6 out of 10 on the Mohs scale. 
Micaceous iron oxide: Has a hardness of 6 on the Mohs scale.
Goethite: Has a hardness of 5.0 to 5.5 out of 10 on the Mohs scale.

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