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Basic or Mafic Igneous rocks

• -There are 3 types of basic igneous rock, GABBRO, DOLEROTE and BASALT. All are composed of the following silicate minerals.
• -Hornblende (10%)
• -Plagioclase feldspar (40%)
• -Augite (30%)
• -Olovine (20%)

Slide 2

• The size of a crystal in an igneous rock is proportional to the length of time the magma took to cool,
• GABBRO is coarse grained: Crystals are generally >5mm and were formed by very slow cooling of magma in a large and well insulated underground magma chamber
• DOLERITE is medium grained: Crystals are between 0.1 to 5mm in size and are formed by the moderately slow cooling of basic magma in a small and shallow intrusion, such as a dyke or sill.
• BASALT is fine grained: Crystals are <o.1mm, which reflects the rapid cooling of surface lava.