sedimentary
Sandstone (Arkose)
Arkose Sandstone (SiO2 with KAlSi3O8)
Hardness: 6-7 Mohs; Color: Pinkish-red, tan, or brown; Luster: Dull to earthy; Texture: Coarse-grained, clastic; Components: High feldspar content (>25%) and quartz.
- Hardness
- 6-7 Mohs
- Color
- Pinkish-red, tan, or brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 Mohs; Color: Pinkish-red, tan, or brown; Luster: Dull to earthy; Texture: Coarse-grained, clastic; Components: High feldspar content (>25%) and quartz.
Formation & geological history
Formed from the rapid weathering and deposition of feldspar-rich igneous or metamorphic rocks (like granite). It typically accumulates in alluvial fans or rift basins where transport distance is short.
Uses & applications
Used as a construction material, building stone, and road aggregate. Historically used for millstones and in some architectural masonry.
Geological facts
Arkose is often called 'dirty sandstone' because of its mineral variety. It is a key indicator for geologists that the sediment source was close by and the climate was likely dry.
Field identification & locations
Identify by its rough, sandpaper-like feel and visible pinkish feldspar grains. Commonly found in sedimentary basins near granitic mountain ranges. Look for quartz and angular grains.
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