Materials of the Earth's Crust - Rocks Notes

EARTH'S CRUST MATERIALS - ROCKS - These rocks are made by the action of seas, rivers, lakes, glaciers, and wind. - Strong, layered rocks are called stratified rocks. - The thickness of these layers changes and they can be slanted or flat. - Sediments are loose bits of gravel, sand, silt, and clay mixed together. - They have holes and let water through. - Loose bits get pressed into hard rocks by sticky stuff like lime or layers on top. - They are separated by flat surfaces. - Lithification is when sediments become sedimentary rocks by sticking together, getting pressed, and hardening. - Sedimentary rocks cover most of the earth's surface. - Sedimentary rocks are also called secondary rocks because they come from the breaking down of older rocks. - When sediments settle in water, they get sorted by size and pile up in different layers. - Each layer has bits of the same size. - Sedimentary rocks have remains of plants and animals between layers, called fossils. - Fossils help tell how old the rocks are. - Sedimentary rocks are grouped by what they are made of, where they came from, and how they formed. ### Sedimentary Rocks Made by Mechanical Action or Clastic Rocks - Mechanical sediments come from breaking down rocks and are called detrital or clastic sediments. - These are bits of gravel, sand, silt, and clay stuck together. - Rounded stones from rivers become conglomerate. - Sharp pieces that gather at the bottom of cliffs get pressed together to form breccia. - Sandstone is a sedimentary rock made from sand. It might have silica or calcium that holds the sand together. It's mostly made of quartz. - Grit is a rough type of sandstone. - Clay deposits form shale or claystone, which has a layered look. - Siltstone is made of silt, which is smaller than sand. - These sediments are grouped by how big the bits are. - Deposits dropped by wind are Aeolian sediments. - Loess is a common example of fine stuff dropped by wind. - It's soft and has holes, is yellowish, and often found in China. ### Sedimentary Rocks Made by Chemical Action - Chemical sediments form when chemicals in water come out of solution. - This happens when water full of minerals dries up on the earth's surface, making chemical rocks. - Rock salt is a chemical sediment that formed when salty water like the Dead Sea, Aral Sea, and Great Salt Lake dried up.