sedimentary
Ferruginous Sandstone Pebble
Arenite with Iron-Oxide Cement (SiO2 with Fe2O3/FeO(OH) staining)
Hardness: 6-7 (on Mohs scale, though variable depending on cementation); Color: Rusty orange/brown to reddish due to iron oxides; Luster: Dull/Earthy (vibrant when wet); Crystal structure: Granular (clastic); Cleavage: None (conchoidal to uneven fracture).
- Color
- Rusty orange/brown to reddish due to iron oxides
- Luster
- Dull/Earthy (vibrant when wet)
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Physical properties
Hardness: 6-7 (on Mohs scale, though variable depending on cementation); Color: Rusty orange/brown to reddish due to iron oxides; Luster: Dull/Earthy (vibrant when wet); Crystal structure: Granular (clastic); Cleavage: None (conchoidal to uneven fracture).
Formation & geological history
Formed through the lithification of sand-sized grains (mostly quartz) in a high-energy environment like a riverbed or beach. The orange color is due to the oxidation of iron minerals (hematite or goethite) within the groundwater that cemented the grains. This specific piece is a 'river cobble,' rounded by mechanical erosion over thousands of years.
Uses & applications
Used primarily in construction as aggregate, for landscaping as decorative river rock, and occasionally by lapidaries as carving material or for 'tumbled' stone collections.
Geological facts
Sandstones like this are part of the 'Red Beds' found globally, which indicate deposition in oxygen-rich environments. The wet appearance in the photo mimics the effect of rock tumbling, revealing the depth of the iron staining.
Field identification & locations
Identify in the field by its gritty 'sandpaper' texture and the presence of visible sand grains. It is commonly found in glacial till, riverbeds, and along shorelines globally. Collectors look for pieces with uniform color or unique weathering patterns.
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