Earth Systems 3209 Reference: Chapters 2, 3, 6, 7; Appendix A & B Unit: 3Earth’s Materials
Unit 3: Topic 4.5 Chemical Sedimentary Rocks Focus on . . . • identifying the processes that form chemical sedimentary rocks. • contrasting precipitates vs. evaporites. • identifying different chemical sedimentary rocks and the environment in which they form.
Chemical Sedimentary Rocks • These rocks form as a result of chemical weathering dissolving chemicals and transporting it in solution. When conditions are right, these dissolved chemicals change back into a solid through the processes of: • Precipitation 2) Evaporation • Evaporation and Precipitation often work together. As water evaporates, chemicals in solution will precipitate.Example: Rock Salt (Halite). • These rocks can also form where ground water dissolves chemicals and precipitates the material in certain environments. • An example of this process would be the formation of stalactites and stalagmites.
ChemicalSedimentary Rocks (Precipitation) • Precipitates • Process where a change in environmental conditions cause chemicals dissolved in solution, to fall out of solution wich forms a solid material. • Results from a change in environmental conditions, such as: • Temperature • Concentration • Chemical changes • Most common in shallow water environments.
Chemical Sedimentary Rocks (Precipitation) • Examples of chemical sedimentary rocks include: • Limestone • 10% of all sedimentary rocks (by volume) • Most abundant chemical sedimentary rock • Composed primarily of calcite (calcium carbonate CaCO3) • Formed by marine organisms (corals, clams, algae) • Some deposited directly out of ocean or other waters • Most abundant chemical precipitate rock which forms in shallow marine waters. Often contain shell fossils.
Chemical Sedimentary Rocks (Precipitation) • Examples of chemical sedimentary rocks include: • 2) Dolomite • CaMg(CO3)2, Calcium Magnesium Carbonate. • Dolomite appears to form in many different types of environments. • Dolomite is used as an ornamental stone and a concrete aggregate. • It is an important Petroleum reservoir rock.
Chemical Sedimentary Rocks (Precipitation) • Examples of chemical sedimentary rocks include: • 3) Travertine • A kind of limestone deposited by springs. • Groundwater traveling through limestone beds dissolves calcium carbonate and as this dissolved matter precipitates it builds up travertine deposits. • "Travertine" is sometimes used to mean cavestone, the calcium carbonate rock that makes up stalactites and other cave formations.
Chemical Sedimentary Rocks (Precipitation) • 3) Travertine • Stalactite:icicle-like pendants that hang from the ceilings of caverns and form where water seeps through cracks above. • Stalagmite:mound shaped deposits that form on the floors of caverns and build upwards toward the ceilings.
Chemical Sedimentary Rocks (Evaporites) • Evaporites • Process where there is a change in state from a liquid to a gas, water evaporates. • Chemicals dissolved in the liquid (water) are left behind as a solid material. • Most common in marine environments, but can also form in some lakes. • Examples include; • Salt (Halite), Gypsum and Sylvite.
Chemical Sedimentary Rocks (Evaporites) • Examples of chemical sedimentary rocks include: • 4) Rock Salt • Consist of the mineral Halite. • Forms by evaporation of shallow seas and lagoons that have high concentrations of halite in solution. The mineral precipitates out of solution as the water evaporates. • Common use is table salt and road salt.
Chemical Sedimentary Rocks (Evaporites) • Examples of chemical sedimentary rocks include: • 5) Rock Gypsum • Consist of the mineral Gypsum. • Forms by evaporation of shallow seas and lagoons that have high concentrations of gypsum in solution. The mineral precipitates out of solution as the water evaporates. • "Common use is plaster and gyproc (drywall).
Example 1: Which is an icicle-like, depositional feature common to cave ceilings? (A) breccia (B) stalactite (C) stalagmite (D) travertine Which is a chemical sedimentary rock? conglomerate (B) limestone (C) sandstone (D) shale
Example 2: Under which condition would a chemical sedimentary rock form? cementing of sand and pebbles compaction of sand and clay (C) hot chemical fluids changing a minerals composition (D) precipitation of dissolved materials into solid form
Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Questions: Using an example, describe the formation of chemical sedimentary rocks.
Solutions . . . Questions: Using an example, describe the formation of chemical sedimentary rocks. Answer: Dissolved chemicals in solution (water) can form solid minerals by precipitating out of solution or as a result of evaporation. Example:Salt water has an accumulation of salt dissolved in the oceans. In shallow marine environments, where water evaporates, the salt (halite) precipitates and forms rock salt.
Summary . . . Overview of Points covered: • Chemical Sedimentary rocks include; • Limestone • Dolomite • Travintine • Rock Salt • Rock Gypsum • Chemical Sedimentary environments include; • Shallow Marine • Deep Marine (Ocean) • Caves