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ROCKS ROCKS • Rocks: naturally occurring combinations of minerals, fossils or other hard materials. • classified by the way in which they form. • 3 rock types: igneous, sedimentary and metamorphic IGNEOUS ROCKS • • vent lava Igneous Rocks: former magma (molten rock), which cooled and crystallized into solid rock Intrusive (Inside) Igneous Rocks: form as magma cools slowly beneath Earth’s surface • lan d surfac e conduit Slow cooling rate allows crystals to grow large, so they are very visible magma • Extrusive Igneous Rocks: form as lava (former magma) cools quickly at Earth’s surface • Anatomy of a Volcano • • Rapid cooling produces small crystals, not readily seen by the unaided eye. Volcanic in origin Cooling may be so rapid that glass is produced (Obsidian) Intrusive Igneous Rocks • Granite: a coarse rock formed from the cooling of magma within the Earth (intrusive) • Composed of various amounts of quartz, feldspar, muscovite, biotite, and hornblende. • Continental crust (that stuff we live on) is primarily composed of granite…know that. quartz biotite mica (*) feldspar Extrusive Igneous Rocks • Basalt: dark, fine-grained igneous rock • • • • Fine grained because it formed quickly or slowly? occurs as lava, sometimes accumulating to thicknesses of 1000s of feet and covering 1000s of miles cools rapidly. Volcanoes which produce basaltic lavas are nonexplosive Oceanic crust is composed of basalt…know this! Igneous Rock Video Basalt – Extrusive Igneous Rock Vesicular Volcanic Bomb (*) Gases released near the surface of a lava flow create bubbles or vesicles, which are “frozen” in stone. Amygdaloidal (*) Basalt – Extrusive Igneous Rock Pahoehoe: feature which forms on the surface of a very fluid basalt flow. Much like the skin on a bowl of tomato soup – the surface in contact with the air begins to crystallize, while the fluid lava below continues to flow. This drags the upper, still plastic, surface into a series of smooth wrinkles. Basalt – Extrusive Igneous Rock The Bottom side of this pahoehoe is rough and jagged and is called Aa. Basalt – Extrusive Igneous Rock Flow banding • Obsidian: volcanic glass • • • • glassy, lustrous and appearance makes it easy to distinguish from all other rocks cooled so quickly that the minerals could not crystallize. Colors vary from black to red, black & red (mahogany), gray, green, iridescent, snowflake. Apache Tears are little nodules of obsidian Apache tear Snowflake SEDIMENTARY ROCKS Sedimentary Rocks: layered or stratified rocks • Sedimentary rocks form from compaction or cementation • Compaction: a squeezing together of particles/sediments • Cementation: particles/sediments get glued together by dissolved minerals • 2 types: Clastic Sedimentary Rock and Chemical Sedimentary Rock • Sedimentary Rocks • Clastic Sedimentary Rocks: composed of particles of preexisting rocks • • • fragments show evidence of transport Examples: Shale, Sandstone Chemical Sedimentary Rocks: composed of solids which precipitated from solutions (like salt from evaporated water) or organic process (like compacted shells from marine organisms) • Examples: Limestone, rock salt, coal Sedimentary Video Sandstone Shale Sandstone and Shale – Sedimentary Rock • Sandstone: composed of cemented sand grains • • • identified by its sandy texture and gritty feel form in beaches, sand bars, deltas and dunes Shale: very common rock made of silt and clay • • • Very thin with splits along the planes. gray to black, or brown to dark red forms in lakes, swamps, and deltas Coconino Sandstone, the result of a Permian age coastal dune field Black shale, from the Middle Cambrian sea. COAL – Sedimentary Rock • Coal: decomposed remains of vegetation which accumulated in a wet, low oxygen environment, such as a swamp or marsh • • Coal (sub-bituminous) out of the Cretaceous Dakota Formation of north-eastern Arizona. Examples include: Peat and Lignite used as fuels Sedimentary Rock • Features of sedimentary rock include: • Layering • ripple marks • mud cracks • salt casts Sedimentary Rock • Features of sedimentary rocks are clues to how the rocks are formed, and help us understand the history of the Earth Weathering, Erosion, and Deposition • Weathering: breaking down of rock through contact with the Earth's atmosphere and waters • Erosion: process by which soil and rock are removed from the Earth's surface by wind or water, and then transported and deposited in other locations Deposition: process by which sediments, soil, and rocks are added or deposited to an area Funny Video • • All rocks on Earth are locked into a system of cycling and re-cycling known as the ROCK CYCLE.