sedimentary
Ferruginous Sandstone
Clastic sedimentary rock (primarily SiO2 with Fe2O3 cement)
Hardness: 6-7 (Mohs scale), Color: Brownish-red to earthy tan, Luster: Dull/Earthy, Crystal Structure: Granular/Clastic, Cleavage: None, Specific Gravity: 2.2–2.8
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Physical properties
Hardness: 6-7 (Mohs scale), Color: Brownish-red to earthy tan, Luster: Dull/Earthy, Crystal Structure: Granular/Clastic, Cleavage: None, Specific Gravity: 2.2–2.8
Formation & geological history
Formed through the accumulation and cementation of sand-sized mineral grains, typically quartz. The distinct brownish-red color comes from iron oxides (hematite or limonite) acting as a binding cement during lithification.
Uses & applications
Used in construction as a building material, road base, and occasionally as decorative garden stone. Certain iron-rich varieties were historically explored as low-grade iron ores.
Geological facts
Sandstone makes up about 20% of all sedimentary rocks on Earth. The 'rust' color is a sign that the rock formed in an oxygen-rich environment where iron could oxidize.
Field identification & locations
Identify in the field by its sandpaper-like texture and visible grains. It is commonly found in desert environments, river beds, and ancient marine basins globally.
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