sedimentary
Arkosic Sandstone
Arkose
Hardness: 6-7 (on Mohs scale); Color: Pinkish-red to tan due to high feldspar content; Luster: Dull/Earthy; Crystal structure: Clastic (grainy texture); Cleavage: None (fractures across grains); Specific gravity: 2.5–2.7.
- Hardness
- 6-7 (on Mohs scale)
- Color
- Pinkish-red to tan due to high feldspar content
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 (on Mohs scale); Color: Pinkish-red to tan due to high feldspar content; Luster: Dull/Earthy; Crystal structure: Clastic (grainy texture); Cleavage: None (fractures across grains); Specific gravity: 2.5–2.7.
Formation & geological history
Formed from the rapid erosion and deposition of granitic rock, preventing the feldspar from weathering into clay. Usually deposited in alluvial fans or rift basins during periods of high tectonic activity.
Uses & applications
Used primarily as decorative building stone, in high-end masonry, and as a source for understanding ancient tectonic environments and mountain-building events.
Geological facts
Arkose is often referred to as 'dirty sandstone' because it contains at least 25% feldspar, unlike pure quartz sandstone. Ayers Rock (Uluru) in Australia is largely composed of arkosic sandstone.
Field identification & locations
Identify in the field by its gritty 'sandpaper' texture and distinctive pink or salmon color. Look for visible crystalline grains of quartz and angular feldspar. Common in mountainous regions with granite outcrops.
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