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Download EHS Rock Classification Guide
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EHS Rock Classification Guide Igneous Rocks – shiny, fresh minerals, no organization Observations: Texture- how big are minerals (coarse or fine)? Are they visible at all? Are minerals visible in some parts of the rock but not everywhere? Color- are there mostly light minerals, mostly dark minerals, or a mix? Minerals – what minerals, if any, can you identify? Color (proportion of light and dark minerals) Key minerals Extrusive/Volcanic Minerals are too small to be seen in some or all of the rock. Some minerals might be visible. Intrusive/Plutonic Minerals EVERYWHERE are large enough to be seen with naked eye. Dark Medium Light Olivine, pyroxene, plagioclase Amphibole Quartz Potassium Feldspar Basalt Andesite Rhyolite Obsidian Black and glassy, no minerals visible Gabbro Diorite Granite Metamorphic Rocks – Shiny fresh minerals, often organized into bands or layers. Observations What is appearance of rock? Shiny sheets? Bands? What minerals can you identify? Metamorphic rocks are classified by their texture and the minerals that are present. Here are a few of the more common metamorphic rocks: Rock Name Schist Gneiss Marble Description Shiny rock with lots of mica. Comes in fine layers. Light and dark bands Large calcite crystals Sedimentary rocks – dull, often made of bits of other rocks Observations how big are the bits of other rocks? Large? Small? Too small to see? How rounded are bits of other rocks? Can you identify minerals? Size of Sediment Other observations Rock Name Environment of formation Larger than sand Angular pieces Breccia Conglomerate Fault zone Sandstone Shale Beach, desert Limestone Till Shallow sea Rounded pieces Sand sized Smaller than Sand Doesn't react with HCl Reacts with HCl Mix of sizes Angular pieces River Bottom lake, mudflats, floodplain Glacier
