sedimentary
Ferruginous Sandstone
Arenite with Iron Oxide cement (primarily Fe2O3)
Hardness: 6-7 on Mohs scale (due to quartz grains); Color: Reddish-brown, rust, or deep chocolate; Luster: Dull/Earthy; Crystal Structure: Clastic texture; Cleavage: None; SG: 2.0-2.6
- Hardness
- 6-7 on Mohs scale (due to quartz grains)
- Color
- Reddish-brown, rust, or deep chocolate
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 on Mohs scale (due to quartz grains); Color: Reddish-brown, rust, or deep chocolate; Luster: Dull/Earthy; Crystal Structure: Clastic texture; Cleavage: None; SG: 2.0-2.6
Formation & geological history
Formed through the accumulation and compaction of sand-sized mineral grains, specifically where iron-rich groundwater or fluids permeate the sediment, depositing hematite or limonite as a cementing agent. Often found in continental or shallow marine environments from various geological ages, notably the Paleozoic and Mesozoic eras.
Uses & applications
Used primarily in building construction as a dimension stone, as decorative landscape rock, and historically as a low-grade iron ore if iron content is high enough.
Geological facts
The distinctive red color is essentially 'rusting' at a geological scale. In many parts of the world, these rocks form iconic landscapes like the Red Rocks in Colorado or the arches in Utah.
Field identification & locations
Identify in the field by its gritty, sandpaper-like texture and its tendency to leave a reddish streak if rubbed against a harder surface. Common in arid environments and sedimentary basins. Collectors should look for interesting layered patterns or inclusions.
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