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IGNEOUS ROCKS by Charina Cameron

IGNEOUS ROCKS by Charina Cameron. Part 2: Textures. TEXTURES. Aphanitic (finely crystalline) Porphyritic (phenocrysts) Phaneritic (coarse) . TEXTURES. Cooling rates control crystal sizes. VOLCANIC GLASS.

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IGNEOUS ROCKS by Charina Cameron

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  1. IGNEOUS ROCKSby Charina Cameron Part 2: Textures

  2. TEXTURES • Aphanitic (finely crystalline) • Porphyritic (phenocrysts) • Phaneritic (coarse)

  3. TEXTURES • Cooling rates control crystal sizes

  4. VOLCANIC GLASS • A glassy texture results from lava cooling very fast at Earth's surface • Obsidian • From a felsic magma • Black in thick pieces from traces of mafic minerals • Conchoidal fracture like window glass

  5. INTRUSIVES - PHANERITIC TEXTURE • Felsic - granite • Intermediate - diorite • Mafic • Phaneritic - gabbro • Aphanitic - basalt

  6. VOLCANICS - APHANITIC TEXTURE • Felsic - rhyolite • Intermediate - andesite • Mafic - basalt

  7. PORPHYRITIC TEXTURES • Phenocrysts = isolated crystals in a finer matrix • Rhyolite porphyry • Andesite porphyry • Basalt porphyry

  8. PYROCLASTICS • Ash (very fine, like flour) • Lapilli (sandy to pebbly) • Bombs (cobble -like & larger) • Volcanic ash • Mount St. Helens (1980)

  9. PYROCLASTICS • Volcanic ash • very fine-grained • can cover everything • Lahars • rain soaks ash • mudflows

  10. CONSOLIDATED PYROCLASTICS • Tuff • Consolidated volcanic ash • Welded tuff = hot ashfused • Banded tuff (with glass)

  11. EVIDENCE OF VOLCANIC GAS • Pumice • Vesicles in lava • Felsic magma • Scoria • Vesicles in basalt • Mafic magma • Hawaii • Amygdaloidal basalt • Vesicles filled with zeolite minerals • Larger & elongated vesicles near top of flow

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