sedimentary
Sandstone (Ferruginous Concretion)
Ferruginous Sandstone Concretion / SiO2 with Fe2O3 cement
Hardness: 6-7 (Mohs); Color: Dark brown, rusty, or tan; Luster: Dull/Earthy; Crystal structure: Clastic/Granular; Cleavage: None; Specific Gravity: 2.6-3.0
- Hardness
- 6-7 (Mohs)
- Color
- Dark brown, rusty, or tan
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark brown, rusty, or tan; Luster: Dull/Earthy; Crystal structure: Clastic/Granular; Cleavage: None; Specific Gravity: 2.6-3.0
Formation & geological history
Formed by the precipitation of mineral cement (typically iron oxides like hematite or limonite) within the spaces between sediment grains, often around a nucleus like a leaf or shell. They range from millions to hundreds of millions of years old.
Uses & applications
Primarily used as geological specimens for education and collecting. In some contexts, iron-rich sandstones are processed as a low-grade iron ore.
Geological facts
They are often mistaken for meteorites or dinosaur eggs due to their symmetrical, rounded shapes. Some are known as 'Moqui Marbles' in the Southwestern United States.
Field identification & locations
Identify in the field by their spherical or discoid shape which contrasts with surrounding softer rock layers. Frequently found in desert environments or eroding out of shale and sandstone cliffs.
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