PETROLOGY

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PETROLOGY

1. Description of rocks
2. Classification of rocks
3. Theories on how these rocks formed

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• Cooling Rates
• Cooling rates influence the texture if the
  igneous rock
• Quick cooling fine grains
• Slow cooling coarse grains

• Crystallize from molten material
• Magma - below the Earth's surface
• Lava - erupts onto the Earth's surface through a
  volcano or crack (fissure)
• Lava cools more quickly because it is on the
  surface.

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EKTRUSIF/VULCONIK (Batuan Beku Luar)

• Terbentuk di permukaan bumi.
• Pembentukan mineral berjalan cepat
• Kristalisasi tidak terjadi/kurang sempurna
• Ukuran mineral tidak dapat dilihat dengan mata.
• Tekstur halus

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INTRUSIF/PLUTONIK (Batuan Beku Dalam)

• Terbentuk jauh di dalam bumi.
• Pembentukan mineral berjalan lambat
• Kristalisasi sempurna
• Ukuran mineral dapat dilihat dengan mata.
• Tekstur kasar

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Igneous textures

• Glassy instantaneous cooling
• Obsidian (volcanic glass)

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• Aphanitic - fine grain size (lt 1 mm) result of
  quick cooling
• Basalt
• Rhyolite
• Andesite

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• Phaneritic - coarse grain size visible grains
  (1-10 mm) result of slow cooling
• Granite
• Diorite
• Gabbro

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• Vesicular - contains tiny holes called vesicles
  which formed due to gas bubbles in the lava or
  magma. Very porous. May resemble a sponge.
  Commonly low density may float on water.

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Composition of Igneous Rocks

1. Felsic (granitic or Sialic )
2. Intermediate (or andesitic)
3. Mafic (or basaltic)
4. Ultramafic

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Felsic (granitic or Sialic )

• Dominated by silicon and aluminum (SiAl)
• Usually light in color
• Characteristic of continental crust
• Rock types include Granite, Riolite
• Accecories mineral potassium feldspar (generally
  pink or white) , Na-plagioclase feldspar
  (generally white) , quartz (generally gray or
  colorless) , biotite

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Intermediate (or andesitic)

• Intermediate in composition between sialic and
  mafic
• Rock types include
• Andesite (aphanitic)
• Diorite (phaneritic)
• Accecories mineral
• plagioclase feldspar, amphibole, pyroxene,
  biotite, quartz

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Mafic (or basaltic)

• Contains abundant ferromagnesian minerals
  (magnesium and iron silicates)
• Usually dark in color (dark gray to black)
• Characteristic of Earth's oceanic crust, Hawaiian
  volcanoes
• Forms a runny (low viscosity) lava
• Rock types include Basalt, Gabbro

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Ultramafic

• Almost entirely magnesium and iron silicates
  (ferromagnesian minerals)
• Rock types include
• Peridotite (phaneritic)
• dominated by olivine - the birthstone is Peridot,
  which gives its name to Peridotite
• Minerals commonly present include
• Olivine is dominant. (Olivine is olive green).
• may have minor amounts of pyroxene and
  Ca-plagioclase

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Order of crystallizationby Dr. N.L. Bowen
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GABBROThis is a mafic igneous intrusive
rock.
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DIORITEThis speckled coarse-grained specimen is
an intermediate composition igneous intrusive
rock.
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GRANITE This is a felsic intrusive rock.
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BASALTThis typically dark, mafic to ultramafic
volcanic rock is apparently featureless. The
presence of olivine suggests it is ultramafic.
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RHYOLITEThe lighter colour is indicative of the
felsic composition of this extrusive rock.
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Kelompok Batuan Beku

1. Rhyolit Granit
2. Trachit- Syenit
3. Dasit-Kwarsa Dasit
4. Andesit-Diorit
5. Gabro-Basalt