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CHAPTER 6.2 IGNEOUS ROCKS IGNEOUS ROCK – FORM FROM THE COOLING OF MOLTEN ROCK EXTRUSIVE (VOLCANIC)- FORM AT OR NEAR THE SURFACE FROM LAVA INTRUSIVE (PLUTONIC) – FORM UNDER THE SURFACE FROM MAGMA TYPES OF MELTS : FELSIC –LIGHT COLORED, HIGH SILICA MAGMA WITH ABUNDANCE OF QUARTZ AND FELDSPAR. THICK SLOW FLOWING IN MOLTEN STATE. MOST INTRUSIVE ROCKS. ACIDIC MAFIC – DARK COLORED, FERROMAGNESIAN MAGMA, MORE FLUID THAN FELSIC MAGMA. MOST EXTRUSIVE IGNEOUS ROCKS. TEXTURE – DEPENDS UPON SIZE, SHAPE AND ARRANGEMENT OF CRYSTALS (GRAINS) GRAIN/CRYSTAL SIZE DEPENDS ON: 1. RATE OF COOLING, SLOWER LARGER 2. GASES – MORE DISSOLVED GASES THE LARGER THE CRYSTAL 3. ORDER OF SOLIDIFICATION, FIRST TO CRYSTALLIZE IS LARGER INTRUSIVE GRANITE GABBRO EXTRUSIVE BASALT OBSIDIAN PORPHYRY RHYOLITE PORPHYRY IGNEOUS FAMILIES - GROUPED ACCORDING TO MINERAL COMPOSITION GRANITE FAMILY – INCLUDE FELDSPAR AND QUARTZ. USUALLY LIGHT COLORED COARSE GRAINED – GRANITE FINE GRAINED – RHYOLITE GLASSY – PUMICE, OBSIDIAN VESICLES – GAS BUBBLES FORM CAVITIES GABBRO FAMILY – FELDSPAR, FERROMAGNESIAN MINERALS COARSE – GABBRO FINE – BASALT DIORITE FAMILY DIORITE ANDESITE DIORITE ANDESITE IGNEOUS INTRUSIONS • PLUTONS – A ROCK MASS THAT FORMS WHEN MAGMA COOLS UNDER GROUND – DIKES – SILLS – LACOLITHS – VOLCANIC NECKS – BATHOLITHS – LARGEST OF ALL PLUTONS, FORM THE CORES OF MOST MOUNTAINS DIKE SILL LACOLITH VOLCANIC NECK BATHOLITH
