sedimentary
Ferruginous Sandstone (River Pebble)
Clastic Sedimentary Rock (primarily SiO2 with Fe2O3 cement)
Hardness: 6-7 (on Mohs scale); Color: Reddish-brown to tan; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.3-2.6
- Hardness
- 6-7 (on Mohs scale)
- Color
- Reddish-brown to tan
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (on Mohs scale); Color: Reddish-brown to tan; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific gravity: 2.3-2.6
Formation & geological history
Formed through the lithification of sand-sized grains, typically quartz. Its reddish color comes from iron oxide (hematite) cementing the grains together. This specimen has been rounded by fluvial (river) or glacial transport over thousands of years.
Uses & applications
Common varieties are used as construction aggregate, road base, and in decorative landscaping. This specific polished pebble has low industrial but high personal/educational value.
Geological facts
Sandstone makes up about 20-25% of all sedimentary rocks on Earth and is a primary reservoir for ground water and oil because of its porosity and permeability.
Field identification & locations
Identify in the field by its gritty 'sandpaper' texture and visible mineral grains. It is commonly found in riverbeds and coastal areas where ancient sedimentary layers have eroded.
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