SEDIMENTARY ROCKS THE EARTH SCIENCE JOURNAL ISSUE 10 NOVEMBER 2013 IN THIS ISSUE Sedimentary Rocks P.1 Bioclastic Rocks P.1 Sediment and Clastic Rocks P.2 Sedimentary Rocks Crystalline Rocks P.2 Sedimentary rocks are unique and varied in nature. They form in one of three ways: (1) from the compaction and cementation of sediments as a clastic rock, (2) from chemical precipitates in solution or evaporates as a crystalline rock, and (3) from compacted plant or animal remains Bioclastic Rocks as a bioclastic rock. Bioclastic rocks are wholly or partial- Clastic rocks are probably the most abundant type of sedimentary rock. Examples include: ly comprised of compacted plant or conglomerate, breccia, sandstone, siltstone, and shale. Each of these 5 rocks are uniquely animal remains. Bioclastic rocks will identified by the sediments that they contain and their characteristics (for more on the 6 types often have fossils within them upon discovery. A classic example of this of sediments, turn to page 2). Clastic rocks form when water surrounding sediments evapo- can be found in samples of coqui- rates and the dissolved minerals in the water act as a cement locking the sediments together. na— a bioclastic rock made up most- ly of shell fragments. This indicates When chemical reactions or evaporation occurs, crystalline rocks may form. Many of the ma- that the environment the rock jor rock salt deposits found in New York State are the result of evaporation of ancient sea- formed in was likely a very shallow water. Limestone and Rock Gypsum are two additional examples of common crystalline rocks. warm-water sea. Bioclastic rocks form from some sort of biological process. A major source of energy for hu- mans (bituminous coal) formed from compacted plant remains and is used to power many power plants across the country. Most sedimentary rocks (with the exception of crystalline rocks) have the potential to form fossils within them and are favorites amongst collectors. Crystalline Rocks Crystalline sedimentary rocks are composed of crystals having formed from a chemical reaction in a solu- tion or from evaporation. The crys- tals can vary in size from very fine (you cannot see them with the na- ked eye) to very coarse. An example of the crystalline rock rock gypsum is pictured below. When crushed and processed it is used to produce dry- wall. Sediment and Clastic Rocks Boulders Boulders are the largest of sediment sizes and are 25.6 centimeters in diameter and larger but are found in relatively few clastic rocks. Cobbles Cobbles are the second-largest sediment size and range from 6.4 centimeters in diameter up to 25.6 centimeters. Pebbles Commonly found in the sedimentary rock conglomerate, pebbles range in size from 0.2 centi- meters in diameter up to 6.4 centimeters in diameter. Sand Sand is the primary ingredient in the sedimentary rock sandstone, and ranges in size from 0.006 cm in diameter up to 0.2 centimeters. Silt and Clay Silt and clay are the smallest sediments before one considers dissolved minerals in water. Silt particles range in diameter from 0.0004 cm to 0.006 cm and clay is less than 0.0004 cm in di- ameter. Both appear to make a stream appear “muddy”, and will remain transported in water with very low velocity. THE EARTH SCIENCE JOURNAL Created By: Dave Burgess Rochester STEM High School I do not own any rights to the images in this journal. All images used for educational purposes only. .