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Igneous Petrology

Formed of interlocking crystals
No foliation or bedding
Formed from the solidification of magma
1. Magma is made from around 40- 50% silica
2. Characterised by high temps of around 600 - 1500 degrees
3. Usually slow flow due to viscosity
The slower the cooling of the magma, the coarser the crystals
Some intrusions will be coarse on the inside and have a fine rim due to cooling next to a chilled margin
Plutonic below 5km then above -hypabyssal and volcanic
Holocrystaline - interlocking crustals
Holohayline - glassy, no crystals
Euhedral - Well formed crystals
Subhedral - Partially well formed
Anhedral - Poorly formed
Primary igneous minerals
1. Feldspars
  1. Mica
    1. Pyroxenes
      1. Amphiboles
        Quartz
Mafic - magnesium and iron rich
Acidic (Felisic) - Light colour
1. Basic - (Mafic) - Dark Colour
Flow banding - crystals aligned due to flow of magma
Spherulitic - radial fibers of quartz and feldspar forming
Vesicular texture - gas bubbles
1. Sometimes infilled with minerals to form amygdaloidal texture
Zenoliths - foreign stones to the magma
Pegmatitic - Coarse grained crystals up to 1 metre

Igneous Petrology

	Created by jess.y1994 over 11 years ago