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PETROLOGY

PETROLOGY. Description of rocks Classification of rocks Theories on how these rocks formed. Crystallize from molten material Magma - below the Earth's surface Lava - erupts onto the Earth's surface through a volcano or crack (fissure)

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PETROLOGY

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  1. PETROLOGY • Description of rocks • Classification of rocks • Theories on how these rocks formed

  2. Crystallize from moltenmaterial • 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. Cooling Rates • Cooling rates influence the texture if the igneous rock: • Quick cooling = fine grains • Slow cooling = coarse grains

  3. 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

  4. INTRUSIF/PLUTONIK (Batuan Beku Dalam) • Terbentuk jauh di dalam bumi. • Pembentukan mineral berjalan lambat • Kristalisasi sempurna • Ukuran mineral dapat dilihat dengan mata. • Tekstur kasar

  5. Igneous textures Glassy=instantaneous cooling Obsidian(volcanic glass)

  6. Aphanitic - fine grain size (< 1 mm); result of quick cooling Basalt Rhyolite Andesite

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

  8. 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.

  9. Composition of Igneous Rocks • Felsic (granitic or Sialic ) • Intermediate (or andesitic) • Mafic (or basaltic) • Ultramafic

  10. 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

  11. 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

  12. 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

  13. 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

  14. MAFIC Order of crystallizationby Dr. N.L. Bowen

  15. GABBROThis is a mafic igneous intrusive rock.

  16. DIORITEThis speckled coarse-grained specimen is an intermediate composition igneous intrusive rock.

  17. GRANITE – This is a felsic intrusive rock.

  18. BASALTThis typically dark, mafic to ultramafic volcanic rock is apparently featureless. The presence of olivine suggests it is ultramafic.

  19. RHYOLITEThe lighter colour is indicative of the felsic composition of this extrusive rock.

  20. Kelompok Batuan Beku • Rhyolit – Granit • Trachit- Syenit • Dasit-Kwarsa Dasit • Andesit-Diorit • Gabro-Basalt

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