Arkose

Arkose

Sedimentary rock
Arkose with K-feldspar (pinkish-orangish) and quartz (gray) grains
Composition
>25% feldspar

Arkose (

Quartz is commonly the dominant mineral component, and some mica is often present. Apart from the mineral content, rock fragments may also be a significant component. Arkose usually contains small amounts of calcite cement, which causes it to effervesce (fizz) slightly in dilute hydrochloric acid; sometimes the cement also contains iron oxide.

Colouration and presence of fossils

Arkose is typically grey to reddish in colour. The sand grains making up an arkose may range from fine to very coarse, but tend toward the coarser end of the scale. Fossils are rare in arkose, due to the depositional processes that form it, although bedding is frequently visible.

Formation process

Arkose is generally formed from the weathering of feldspar-rich

• 
  Arkosic sand in the Llano Uplift, Texas, with granite outcrops
• 
  Grus sand and the granitoid it's derived from

Uluru

The central Australian inselberg Uluru (Ayers Rock) is composed of late Neoproterozoic/Cambrian arkose, deposited in the Amadeus Basin.^[4]

See also

• Lithic sandstone – Sandstone with fragments of other rocks

References