sedimentary
Red Sandstone
Arenite (with Iron Oxide / Hematite), Formula: SiO2 (Quartz) + Fe2O3 (Hematite coating)
Hardness: 6-7 (Quartz grains) but often friable; Color: Reddish-brown, terracotta, or pink; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None (fractures around grains); Specific Gravity: 2.2 - 2.8
- Hardness
- 6-7 (Quartz grains) but often friable
- Color
- Reddish-brown, terracotta, or pink
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Quartz grains) but often friable; Color: Reddish-brown, terracotta, or pink; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None (fractures around grains); Specific Gravity: 2.2 - 2.8
Formation & geological history
Formed through the accumulation and cementation of sand-sized mineral grains or rock fragments. The red color indicates formation in an oxygen-rich environment where iron minerals oxidized (rusted). Often found in ancient desert dunes or river delta systems ranging from Paleozoic to Mesozoic eras.
Uses & applications
Widely used as a building material and decorative stone (brownstone). Used in landscaping, glass manufacturing (if high purity silica), and as an abrasive in industrial applications.
Geological facts
Famous red sandstone formations include the Grand Canyon's layers, the 'Red Rocks' of Colorado, and the ancient city of Petra in Jordan, which was carved directly into red sandstone cliffs.
Field identification & locations
Identify in the field by its gritty, sandpaper-like feel and visible layering (bedding). It will not fizz with acid unless it has a rare calcite cement. Commonly found in arid regions or uplifted sedimentary basins.
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