sedimentary
Ferruginous Sandstone (with Iron Oxide staining)
Clastic Sedimentary Rock - Quartz Arenite/Wacke
Hardness: 6-7 (Mohs scale for individual quartz grains); Color: Reddish-brown, rusty orange, and dark grey; Luster: Dull/Earthy; Crystal structure: Granular/Clastic texture; Cleavage: None (fractures around grains).
- Hardness
- 6-7 (Mohs scale for individual quartz grains)
- Color
- Reddish-brown, rusty orange, and dark grey
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs scale for individual quartz grains); Color: Reddish-brown, rusty orange, and dark grey; Luster: Dull/Earthy; Crystal structure: Granular/Clastic texture; Cleavage: None (fractures around grains).
Formation & geological history
Formed through the accumulation, compaction, and cementation of sand-sized mineral grains or rock fragments. The reddish-brown coloration is due to the presence of iron oxide (hematite or limonite) acting as a cementing agent or staining the grains. These often date from the Paleozoic to Mesozoic eras depending on the local basin.
Uses & applications
Used primarily as construction aggregate, low-grade building stone, or decorative landscaping rock. Some variants with high iron content were historically used as iron ore (bog iron).
Geological facts
Iron-rich sandstones are what give the American Southwest its famous red rock landscapes, such as those in Sedona or the Grand Canyon. The color is essentially 'rust' on a geological scale.
Field identification & locations
Identify in the field by its sandpaper-like gritty feel and the way it may leave a reddish streak if rubbed against a harder white surface. Common in riverbeds, glacial till, and sedimentary basins. It is often found as 'float' (loose rock) in areas with eroded sandstone bedrock.
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