sedimentary
Banded Sandstone
Arenite (composed primarily of Quartz: SiO2)
Hardness: 6-7 on Mohs scale; Color: Reddish-brown, tan, and purple banding; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific Gravity: 2.2-2.8
- Hardness
- 6-7 on Mohs scale
- Color
- Reddish-brown, tan, and purple banding
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Reddish-brown, tan, and purple banding; Luster: Dull/Earthy; Crystal structure: Granular/Clastic; Cleavage: None; Specific Gravity: 2.2-2.8
Formation & geological history
Formed through the accumulation and cementation of mineral grains (mostly quartz) in ancient riverbeds or coastal environments. The banding represents 'cross-bedding' or rhythmic deposition layers, likely from the Phanerozoic eon. This specific specimen has been water-shaped and smoothed into a 'cobble'.
Uses & applications
Used primarily as decorative stone, aquarium landscaping, or building material (when in brick form). Occasionally used for low-cost lapidary work like rock tumbling.
Geological facts
The distinct purple and red hues are caused by varying concentrations of iron oxide (hematite) and manganese during the lithification process. Water-worn stones like this are often referred to as 'river rocks' or 'beach cobbles'.
Field identification & locations
Identify in the field by the visible sand-sized grains and the characteristic layered 'stripes' that do not wrap completely around like a vein would. Common in sedimentary basins, river mouths, and glacial till. For collectors, look for high color contrast between bands.
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