Cooling

• Granite cools slowly within the Earth's crust. Feldspar, quartz and mica crystals form during the cooling. Vertical and horizontal fissures form within the rock mass as it contracts. The fissures expand to larger fractures as the rock cools further.
  
  

Wind

• Wind, water and ice denude the soil and Earth's crust overlying the granite mass, exposing it to the atmosphere. The rock expands and contracts in reaction to changes in temperature. It shatters on the surface and the fractures widen to form crevices.
  
  

Hydrolysis

• Hydrolysis is the chemical weathering of minerals by a mildly acidic water that forms when rains dissolves trace gases in the atmosphere. The reaction of feldspar minerals in granite with rainwater produces kaolinite, white clay known as "China clay" used in the production of porcelain, paper and glass. Kaolinite is most abundant over weathered granite in hot and moist tropical climates. Biotite and muscovite micas also weather by hydrolysis into kaolinite and release iron, potassium and magnesium into the surrounding soil as nutrients.
  
  

Quartz

• Sand dunes in the White Sands National Monument, New Mexico are weatherd grains of quartz.Tom Brakefield/Stockbyte/Getty Images
  
  Quartz is very resistant to weathering. It cools down within the granite to form clear crystal veins. Trace iron colors the quartz pink to create rose quartz. Copper colors quartz green to form beryl. Hydrocarbon "seeps" color quartz violet to create amethysts. Rose quartz, beryl and amethyst are semiprecious stones. Smaller quartz crystals remain as grains in the soil or accumulate as sand on river banks and shorelines.