sedimentary
Sandstone (Ferruginous)
Sandstone (primarily SiO2 with iron oxide Fe2O3 staining)
Hardness (Mohs scale): 6-7; Color: Reddish-brown, tan, orange from iron oxidation; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.2-2.8
- Color
- Reddish-brown, tan, orange from iron oxidation
- Luster
- Dull/Earthy
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Physical properties
Hardness (Mohs scale): 6-7; Color: Reddish-brown, tan, orange from iron oxidation; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.2-2.8
Formation & geological history
Formed from the accumulation and cementation of sand-sized mineral particles or rock fragments over millions of years in environments like deserts, riverbeds, or beaches. The iron staining occurs as groundwater rich in iron minerals percolates through the porous rock.
Uses & applications
Used in construction as a building stone, for paving, in the manufacture of glass (if high quartz content), and as a common decorative landscaping stone.
Geological facts
Sandstone makes up about 20% of all sedimentary rocks on Earth. The iron oxide that gives it the red/orange color is the same chemical compound found in rust.
Field identification & locations
Identify in the field by its gritty, sandpaper-like feel and visible grains. Often found in layered outcrops or river valleys. Useful for collectors as a sturdy, colorful specimen of sedimentary layering.
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