sedimentary
Sandstone (Ferruginous)
Arenite (primarily SiO2 with Fe2O3 inclusions)
Hardness: 6-7 (Mohs); Color: Tan, brown, and reddish-orange due to iron oxidation; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific Gravity: 2.2-2.8
- Hardness
- 6-7 (Mohs)
- Color
- Tan, brown, and reddish-orange due to iron oxidation
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Tan, brown, and reddish-orange due to iron oxidation; 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 silicate grains. The iron-rich staining suggests formation in an oxygenated environment where minerals like hematite or limonite leached into the sand body. Geological age can range from Precambrian to Holocene.
Uses & applications
Commonly used in construction as a building stone or road base. In industrial terms, crushed sandstone provides silica for glassmaking. Smooth river-worn specimens like this are often kept as decorative 'pocket stones' or garden accents.
Geological facts
Sandstone makes up about 20% of all sedimentary rocks on Earth. The reddish 'rust' seen on the surface is a result of iron minerals oxidizing, much like a piece of metal rusting in the rain.
Field identification & locations
Identifiable by its gritty, sandpaper-like texture and visible layers (bedding planes). Frequently found in riverbeds, deserts, and coastal cliffs. To identify in the field, look for the 'sand' feel when rubbed and the lack of crystalline spark compared to igneous rocks.
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