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Rocks Chapter 4 Classifying Rocks Mineral Composition - Look with a magnifying glass to determine the mineral that makes up the rock Color - Light or dark color, glassy? Texture – look and feel of the rocks surface Grain size – Fine, coarse or no visible grain Grain Shape – Rounded or jagged Grain Pattern – non-banded, banded Rocks is a rock? mixture of minerals, mineraloids, glass or organic matter 3 Types of Rocks: 1. Igneus Rock – molten material inside earth or from a volcano cools slowly due to the insulation of rock allowing the atoms to arrange themselves into large crystals called mineral grains What Remember: magma forms from great temperatures (1400oC) and pressure in the earth this melts the minerals and forms magma When magma flows to the surface it is called lava Intrusive Rocks Intrusive Rocks– formed when magma insulated and trapped below the earth surface, holds heat and cools slowly – large mineral grains Granitic – light colored rocks, lower density contains a lot of silicon and oxygen, mountains Extrusive Rocks Extrusive Rocks – Formed when magma cools on the earths surface and cools rapidly – fine grained texture Basaltic – dense, heavy, dark colored (magma) examples iron, magnesium, covers ocean floor Combination: Andresitic – in between basaltic and granitic in mineral composition Igneous Rocks - Texture Intrusive—Large crystals Extrusive—Small Crystals (maybe not visible: obsidian & Pumice) Mafic—Dark Felsic—Light Obsidian Pumice Andesite Rhyolite Diorite-Dark color w/ large black crystals Basalt Gabbro Granite Sedimentary Rock Sedimentary rock -comprises 75 % rocks on earth -formed when sediments pressed or cemented together – may form layers Sediments – loose materials such as rock fragments, grains and bits of plant and animals Compactation – pressure causes sediments to form rock Cementation – water dissolves minerals (quartz, calcite, hematite, limonite) natural cements Classification of sedimentary rock: Clastic – broken, named for size & shape of sediments example – conglomerate, breccia, sandstone, shale Chemical – minerals precipitated from a solution or evaporates example – limestone, rock salt Organic – from once living things examples – coal, chalk Sedimentary Rocks Compacted or Cemented (layering is key) Sandstone Shale Coal (rock or not? Some debate) Clastic Breccia—sharp angles Conglomerate—rounded edges (concrete) Coquina—Shells Coal Sandstone Mudstone-gray & silky soft Shale Conglomerate Breccia Coquina Coral Reefs Formed from skeletons of tiny coral animals that grow together to form the coral reef structure Almost all coral reef growth occurs within the top 40 meters of the surface where sunlight penetrates Coral organisms need warm water, found only in tropical oceans Limestone deposits formed from coral reefs Metamorphic Rock Metamorphic rock – rocks changed due to temperature and pressure increases or change in composition Classification of Metamorphic Rock Foliated – mineral grains flatten and line up in parallel bands Example slate and gneiss Slate forms from shale which is arranged in layers when exposed to heat and pressure Nonfoliated – no banding occurs, the mineral grains change, grow and rearrange but no bands Example is marble which forms from sedimentary rock calcite – shiny. Hornblende and serpentine – green. Hermatite - red Metamorphic Rocks Gneiss—Zebra strips Schist—Metallic shine Marble—Contains Calcite (bubbles w/HCl) Or Morphed sedimentary rock Slate (shale that has hardened) Gneiss Slate Schist Marble Phyllite Rock Cycle