What happens when granite is weathered?
• First, unweathered granite contains these minerals: • Na Plagioclase feldspar • K feldspar • Quartz • Lesser amounts of biotite, amphibole, or muscovite • The feldspars will undergo hydrolysis to form kaolinite (clay) and Na and K ions • The Na and K ions will be removed through leaching • The biotite and/or amphibole will undergo hydrolysis to form clay, and oxidation to form iron oxides. • The quartz (and muscovite, if present) will remain as residual minerals because they are very resistant to weathering. • Weathered rock is called saprolite • Weathered rock fragments are one of the constituents of soil. • What happens after this? • Quartz grains may be eroded, becoming sediment. The quartz in granite is sand-sized; it becomes quartz sand. The quartz sand will ultimately be transported to the sea where it accumulates to form beaches. • Clays will ultimately be eroded and washed out to sea. Clay is fine-grained and remains suspended in the water column; it may be deposited in quiet
