sedimentary
Sandstone (Arkose)
Arkose Sandstone (principally SiO2 with Feldspar)
Hardness: 6-7 (Mohs scale), Color: tan to reddish-brown, Luster: dull/earthy, Crystal structure: clastic (granular), Cleavage: none, Specific gravity: 2.2-2.8
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Physical properties
Hardness: 6-7 (Mohs scale), Color: tan to reddish-brown, Luster: dull/earthy, Crystal structure: clastic (granular), Cleavage: none, Specific gravity: 2.2-2.8
Formation & geological history
Formed from the weathering of feldspar-rich igneous or metamorphic rocks (like granite). It occurs through rapid deposition in terrestrial basins, often during the Phanerozoic eon. High feldspar content suggests short transport distances.
Uses & applications
Used primarily as a building material, road base, or abrasive. Fine specimens are used in landscape architecture.
Geological facts
Arkose is often called 'feldspathic sandstone' because it must contain at least 25% feldspar. It often indicates a nearby mountain-building event where granite is being eroded.
Field identification & locations
Identify by its 'sandpaper' texture and visible pink/white feldspar grains. Commonly found in rift valleys and alluvial fans. Collectors look for well-defined bedding planes or cross-bedding features.
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