NOTES: Sedimentary ROCKS AIM: What are the characteristics of sedimentary rocks? 1. Sedimentary rocks are formed from the accumulation and lithification of sediments. 2. There are 3 types of sedimentary rocks: Clastic sedimentary rocks are formed from clay, sand, and gravel (fragments) Crystalline sedimentary rocks are formed from mineral grains and crystals that precipitate out of solution by evaporation or chemical action Bioclastic or Organic rocks are formed from the remains of plants and animals 3. Clastic Rocks – the particles consist of weathered existing rocks. Particle sizes vary 1 Large accumulations of clastic sediments exist where rivers meet still bodies of water Clastic rocks are lithified by compaction and cementation Compaction occurs when the weight of overlying sediments compresses the material and squishes out most of the water 2 Cementation occurs when dissolved minerals precipitate in the pores between the particles and glue them together. Ex: silica, calcite, hematite 4. Crystalline Rocks – the minerals dissolved in solution are precipitated from water by evaporation or chemical action. 5. Bioclastic or Organic rocks are formed from accumulations of remains of living things. YES, rocks made of dead stuff. 3 6. Secondary Sedimentary Features: see these in a rock and it’s probably sedimentary. a) Stratification – the arrangement of sedimentary rock in visible layers that may separate easily b) Fossils – the remains, impressions, or any other evidence of the existence of life preserved in the rock Ex: 4 c) Ripple Marks – seen on the surface of a bed of sandstone formed from wave action on the sand sediment before lithification d) Mud Cracks – these develop when deposits of wet clay dry out and crack. Cracks often fill with different material 5 6 7