sedimentary
Sandstone (specifically an Iron-Concretion)
Arenite with Iron Oxide (Limonite/Goethite) cementation
Hardness: 6-7 on Mohs scale (due to quartz grains); Color: Reddish-brown, tan, or dark dark chocolate brown; Luster: Dull, earthy; Crystal structure: Granular/clastic grains; Cleavage: None; Specific gravity: 2.2 - 2.8.
- Hardness
- 6-7 on Mohs scale (due to quartz grains)
- Color
- Reddish-brown, tan, or dark dark chocolate brown
- Luster
- Dull, earthy
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Physical properties
Hardness: 6-7 on Mohs scale (due to quartz grains); Color: Reddish-brown, tan, or dark dark chocolate brown; Luster: Dull, earthy; Crystal structure: Granular/clastic grains; Cleavage: None; Specific gravity: 2.2 - 2.8.
Formation & geological history
Formed through the accumulation and compaction of sand-sized mineral particles or rock fragments. The dark coloring suggests iron oxide precipitation within the pore spaces between grains, often forming nodules or concretions in sedimentary basins over millions of years.
Uses & applications
Common sandstone is used in construction and paving. Iron-rich nodules are primarily collected as geological curiosities or 'souvenir stones'. In some cases, high-purity sandstone is used for glass making.
Geological facts
Sandstone makes up about 20% of all sedimentary rocks on Earth. This specific dark, rounded appearance is often mistaken for meteorites by amateur collectors due to its weight and dark iron crust (regmaglypts-like texture).
Field identification & locations
Identify in the field by its gritty 'sandpaper' texture and the presence of layering (bedding). This specimen is a iron-stained nodule, often found in 'badlands' or desert environments where softer surrounding rock has eroded away.
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