HKDSE Geography/E1/Igneous Rocks

Formation

 * 1) Magma in the mantle is under great pressure.
 * 2) When a line of weakness appears in the crust and reaches the magma chamber below the magma pressure is released.
 * 3) Magma rises along the cracks to the earth's surface (extrusive/volcanic rock) or inside the earth's crust (intrusive rock)
 * 4) The magma cools and solidifies. Crystallisation occurs in the process. Interlocking crystals are formed.

Granite
A plutonic rock, granite is made of three minerals: quartz (clear/milky), mica (black) and feldspar (pink/grey). These minerals occur as interlocking crystals with coarse or medium-sized grains. It is a well-jointed rock and light in colour.