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Lecture 2 Notes - Yellowstone park includes a large caldera...

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Yellowstone park includes a large “caldera”, which is a large crater caused by the collapse of a gigantic magma chamber. Yellowstone is still very active.
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Yellowstone has had multiple caldera eruptions
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Igneous rocks are classified by: 1. Texture (The size of the mineral crystals) 2. Composition (What minerals it is made of) Review
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texture The slower that molten rock cools, the larger the mineral crystals tend to be. Magma cools very slowly beneath the Earth’s surface, so the mineral crystals are large and visible to the naked eye. Lava is exposed to the cool surface air and/or water, so it cools very quickly . Because it cools quickly, the mineral crystals are usually microscopic . Lava cooled quickly - microscopic crystals magma cooled slowly - large crystals Review
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Textures : Fine-grained (results from fast cooling of extrusive igneous rocks) Course-grained (results from slow cooling of intrusive igneous rocks) Porphyritic (mixed texture – some small grains, some large) Glassy (results from very rapid cooling of extrusive igneous rocks) Fine-grained Course-grained Glassy Porphyritic Review
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Common Igneous Rock Minerals Quartz Feldspar Muscovite Biotite Amphibole Pyroxene Olivine Felsic Mafic Composition Higher Silicon Percentage Lower Silicon Percentage Review
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Mafic Igneous Rocks Lower Silicon Concentrations Higher Melting Temperature Lower Viscosity (flows easily) Dark Colored (black) Felsic Igneous Rocks Higher Silicon Concentrations Lower Melting Temperature Higher Viscosity (does not flow easily) Light Colored (pink and/or gray) Light-colored felsic rock dark-colored mafic rock Color is very helpful in determining whether a rock is felsic or mafic! Review
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THESE ARE THE EXAMPLES THAT YOU MUST KNOW! Felsic Mafic Fine- grained texture (extrusive) rhyolite basalt Course- grained texture (intrusive) granite gabbro Review
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If a rock is made of mostly olivine (which is the most mafic mineral), then we say it has an “ultramafic” composition. A rock with an ultramafic composition is called a “peridotite”. Peridotite is made of mostly olivine and often contains a little bit of pyroxene. The mantle is made of peridotite (the green rock we passed around).
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Common Igneous Rock Minerals Quartz Feldspar Muscovite Biotite Amphibole Pyroxene Olivine Felsic Mafic Composition Review Granites and rhyolites are made of mostly: Quartz, feldspar, muscovite, biotite, and amphibole. Gabbros and basalts are made of mostly: Amphibole, pyroxene, and olivine Peridotite is mostly made of olivine and a little bit of pyroxene. Most mafic Most felsic
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In many volcanic eruptions, the lava explodes out of the Earth. The lava solidifies before it hits the ground. These pieces of solidified lava are called pyroclasts .
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