Tuesday, February 08, 2011

Igneous Rock

Igneous Rock

It happens from magma (molten rock) that undergoes a cooling process, then freezes. Based on the freezing process, igneous rocks are divided into three kinds, those are:

1. Inner Igneous Rock

The freezing happens inside, very deep under the Earth’s surface. Its cooling process is very slow. This causes the formation of big, perfect, and compact mineral crystals. The structure of mineral like that is called plutonic structure or granite (holocrystaline). Inner igneous rock is called also abisis rock. For example: granite rock, diorite, synite, and gabro.

2. Igneous Rock or Hypabyssal Rock

The remain of magma permeates into the upper layer and intrudes to the cracks of volcanic tunnels, then it becomes cool and freezes. The freezing process is relatively faster, so crystals that happen are not as compact as inner igneous rock. The structure of this igneous rock is called porphyry structure. For example: granite, diorite porphyry, syenite porphyry, and porphyry.

3. Outer igneous rock or effusive igneous rock

Igneous rock of this kind happens from magma that reaches the Earth’s surface, then it freezes. Its freezing process is rapid, so crystal can be formed. For example, in porphyry texture.

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