Arkose is a distinctive, K-feldspar-rich, siliciclastic sedimentary rock. It is usually a breccia or sandstone. Arkoses have easily recognized clasts of pinkish- to orangish- to salmon-colored material - that's the K-feldspar. Some arkoses have an overall dark red coloration. Arkoses are not exclusively composed of K-feldspar, however - there is a significant component of quartz.
Arkoses were generally deposited near their sediment source. Source areas had fairly significant topographic relief and had extensive exposures of granites. Large K-feldspar crystals are only common in granites, so the source areas for arkoses had to include extensive outcrops of felsic intrusive igneous rocks.
Arkose with K-feldspar (pinkish-orangish) and quartz (gray) grains.