Arkose
“The feldspar-rich sandstone”
Sedimentary
Arkose is a coarse-grained sandstone containing at least 25% feldspar, giving it a distinctive pinkish or reddish color. It typically forms in arid environments where rapid erosion of granite deposits the sediment before feldspar can fully break down into clay.
Composition
feldspar (25%+), quartz, mica, rock fragments
Where Found
Fountain Formation (Colorado, USA), Torridonian Sandstone (Scotland), Uluru/Ayers Rock (Australia)
Mohs Hardness
6-7
Fun Fact
Uluru (Ayers Rock), one of the world's most iconic natural landmarks, is composed largely of arkose — its famous red color comes from iron-oxide-coated feldspar grains.
Test Your Knowledge
What does arkose's high feldspar content tell geologists about its depositional environment?
Related Specimens
Want to identify rocks yourself?