ROCKS ROCK • Classified on the basis of FORMATION • 3 Types – Sedimentary – Igneous – Metamorphic 3/15/2016 Rocks • Composed of Minerals – Mixtures • 2 Types – Monomineralic – Polymineralic • Of the 4000 minerals, only 8 of them make up 90% of the crust. 3/15/2016 Sedimentary Rocks • Rocks that form from the accumulation of sediments, organic material or chemical precipitates. 3/15/2016 Three main types • Clastic –Made from fragments of other rocks • Chemical/non-clastic • Organic 3/15/2016 Clastic (also known as fragmental) • Classified on the basis of grain size • Formation–Compaction (Pressure) –Cementation (glued) Examples –calcite –silicate 3/15/2016 1. Layers of sediments accumulate 2. Pressure squeezes lower layers 3. Sediment becomes compacted and cemented into rock Pressure = Limestone 3/15/2016 Pressure = shale Pressure = Sandstone 3/15/2016 3/15/2016 Non-clastic (chemical) sedimentary rocks • Formed from evaporation of water – Examples • limestone • Halite • Also known as evaporites • Precipitates also occur 3/15/2016 Organic Sedimentary Rocks • Formed from the remains of former living things –Example: coal 3/15/2016 3/15/2016 Sedimentary Rocks • Chemical and organic sedimentary rocks identified primarily by composition and texture (grain size) • Sedimentary rocks form relatively close to the Earth’s surface Why? 3/15/2016 Sedimentary Rocks • All clastic sedimentary rocks are formed in horizontal layers Why do you think this is so? 3/15/2016 3/15/2016 Bedding in Sandstone and Shale, Utah Crossbedded Sandstone, Zion Natl. Park, Utah. Formed by Sand dunes deposited by wind Graded Bedding Sedimentary Rocks • Sedimentary rocks sometimes contain fossils –Igneous and metamorphic rocks almost never do Why not? 3/15/2016 Sedimentary Rocks • Lake and ocean environments produce different sedimentary rocks –Examples: • Limestone –Forms in oceans • Sandstone –Forms in water near land 3/15/2016 3/15/2016 Use your ESRT to answer the following questions. • What is the composition of rock salt? • What is the size range of the grains in sandstone? • Draw the map symbol of shale • Which is made of rounded fragments, conglomerate or breccia? 3/15/2016