sedimentary
Sandstone (Ferruginous)
Ferruginous Sandstone (SiO2 with iron oxide cement)
Hardness: 6-7 (Mohs); Color: Brown, reddish-brown, tan; Luster: Dull/Earthy; Crystal structure: Clastic (granular); Cleavage: None; Specific Gravity: 2.2–2.8
- Hardness
- 6-7 (Mohs)
- Color
- Brown, reddish-brown, tan
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Brown, reddish-brown, tan; Luster: Dull/Earthy; Crystal structure: Clastic (granular); Cleavage: None; Specific Gravity: 2.2–2.8
Formation & geological history
Formed from the lithification of sand-sized grains (mostly quartz) in environments like deserts, riverbeds, or beaches. The brown color indicates iron oxide (limonite or hematite) acting as the cementing agent. Geological age varies widely from Precambrian to Cenozoic.
Uses & applications
Commonly used as a building material (brownstone), paving, and historically for grinding stones. Also acts as an important reservoir rock for groundwater and petroleum.
Geological facts
Sandstone makes up about 10-20% of all sedimentary rocks on Earth. The Great Sphinx of Giza is carved primarily from limestone, but many other ancient structures like Petra are famous for their sandstone architecture.
Field identification & locations
Identify in the field by its gritty texture (feels like sandpaper) and visible layering (bedding). Found worldwide in sedimentary basins. Collectors look for unique banding (wonderstone) or fossil inclusions.
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