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Rocks Sedimentary Metamorphic Igneous Sedimentary Rock • Clastic – fragments of rocks and minerals that have been physically transported and deposited and then converted into rock • Chemical – Direct precipitation of minerals from a solution • Biochemical/Organic- Remains of plants and animals that have been converted into rock Rocks Metamorphic Sedimentary Clastic Chemical Igneous Biochemical/organic Clastic Sedimentary Rock • Made up mostly of fragments called clasts (means broken) that are eroded from other rocks. Angular clasts = breccia Clasts Rounded clasts = conglomerate Clastic Sedimentary Rock Classified by the sizes of their particles • Coarse-grained; Gravel (pebbles to boulders, bigger than 2mm) – conglomerates and breccia • Medium-grained; Sand (1/16 to 2 mm) – sandstone, porous • Fine-grained; Mud or clay (1/16 mm or smaller) – siltstone and shale, non-porous Rocks Metamorphic Sedimentary Clastic Chemical Coarse-grained Medium-grained Fine-grained Sandstone Conglomerates, breccia Siltstone, shale Igneous Biochemical/organic Chemical Sedimentary Rock • Rocks consist of materials that have precipitated from water in oceans, lakes, caves, or hot springs • Precipitation: the process of forming solid mineral constituents from a solution • Evaporites are chemical sedimentary rocks that form due to evaporation of a solution – e.g. salt (NaCl) and travertine (CaCO3) Chemical Sedimentary Rock Utah’s Bonneville Salt Flats Copyright © Bruce Molnia, USGS Rocks Metamorphic Sedimentary Clastic Coarse-grained Chemical Igneous Biochemical/organic Medium-grained Fine-grained Sandstone Conglomerates, breccia Siltstone, shale Limestone, chert, gypsum, rock salt Biochemical or Organic Sedimentary Rock • Sediments consist mainly of the remains of organisms • Usually forms in underwater environments • Marine: plant and animal debris, especially shells, are compressed and cemented to form chert, limestone, chalk, etc. • Non-marine: Plant debris deposited in freshwater swamps is compressed to form coal Rocks Metamorphic Sedimentary Clastic Coarse-grained Chemical Igneous Biochemical/organic Medium-grained Fine-grained Limestone, chert, chalk, coal Sandstone Conglomerates, breccia Siltstone, shale Limestone, chert, gypsum, rock salt Classification • Classification = the grouping of objects by similar features – Makes it easier for people to think about and discuss what they are investigating • Distinguishing features help us classify things – for rock samples, these include grain size, grain shape, what minerals the rock is made of, fossils, textures, streaks, and more Rocks Sedimentary Clastic Coarse-grained Metamorphic Chemical Igneous Biochemical/organic Medium-grained Fine-grained Limestone, chert, chalk, coal Sandstone Conglomerates, breccia Siltstone, shale Limestone, chert, gypsum, rock salt
