sedimentary
Ferruginous Sandstone (Gerrit)
Arenite with Iron Oxide cementation
Hardness: 6-7 (individual quartz grains), Color: reddish-brown to tan due to iron oxidation, Luster: dull to earthy, Crystal Structure: granular clastic texture, Cleavage: none.
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Physical properties
Hardness: 6-7 (individual quartz grains), Color: reddish-brown to tan due to iron oxidation, Luster: dull to earthy, Crystal Structure: granular clastic texture, Cleavage: none.
Formation & geological history
Formed via the accumulation of sand-sized grains (mostly quartz) in river, lake, or ocean environments, subsequent burial, and cementation by iron minerals such as hematite or goethite.
Uses & applications
Used as a building stone (brownstone) in architecture, industrial sand source if pure, and commonly collected as a decorative garden or landscape rock.
Geological facts
Iron-rich sandstones are often referred to as 'brownstones' in American architecture and are famous for the iconic row houses in NYC. The reddish color is essentially 'rust' on the grains.
Field identification & locations
Identify by its gritty texture (feels like sandpaper) and its distinctive reddish staining that doesn't wash off. Commonly found in terrestrial depositional basins and along ancient riverbeds.
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