sedimentary
Ferruginous Sandstone (Iron-rich Sandstone)
Ferruginous Arenite
Hardness: 6-7 on Mohs scale; Color: Brown, reddish-brown, or ochre; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.2-2.8
- Hardness
- 6-7 on Mohs scale
- Color
- Brown, reddish-brown, or ochre
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Brown, reddish-brown, or ochre; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.2-2.8
Formation & geological history
Formed through the accumulation of sand-sized grains (mostly quartz) that are cemented together by iron oxides like hematite or limonite. It typically forms in fluvial, deltaic, or shallow marine environments where iron-rich water interacts with sediment.
Uses & applications
Commonly used as a building stone (dimension stone), road base material, and occasionally as a source of low-grade iron ore. In some cultures, the iron-rich portions (ochre) are used as natural pigments.
Geological facts
The red colors of the Grand Canyon and Ayers Rock (Uluru) are primarily due to the presence of iron oxides (rust) coating the sand grains in sandstone. This specimen shows 'rinds' or crusts that are typical of chemical weathering.
Field identification & locations
Identify in the field by its gritty, sandpaper-like texture and the characteristic orange-brown 'rusting' color. It is found worldwide in sedimentary basins. Collectors should look for unique weathering patterns or fossils within the layers.
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