Rock Cycle Sedimentary, Igneous, Metamorphic
What is a rock? -A naturally formed solid that is usually made up of one or more types of minerals. - A few types of rocks are made of one mineral or no minerals. - ex: Limestone can be made entirely of calcite - ex: Obsidian contains no minerals - ex: Coal is made up of ancient plants pressed into rock
Igneous Rocks - Intrusive - Rocks that form when magma cools within the Earth - Large crystals can form because: • the interior of Earth is very hot • the high temps allow magma to cool slowly • slow cooling allows time for large mineral crystals to form - Examples are: Granite and Gabbro
Igneous Rocks - Extrusive - Rocks that forms when lava cools on Earth’s surface - Very small crystals form because: • the surface of Earth is cooler than Earth’s interior • the lower temps cause lava to cool quickly • there is no time for large mineral crystals to form - Examples are Rhyolite, Pumice and Basalt
Sedimentary Rocks - Sediments are materials that settle out of water or air. - Sedimentary rocks develop from layers of sediments that build up on land or underwater. - Sediments can be put under pressure or cemented together by new minerals to form rock. - Some rocks, like coal and limestone, form from plants and fossils. - Some rocks can dissolve and re-form as the water evaporates. - Geologists find that rocks with ripples (crossbeds) are preserved because sand once moved along that surface. Mud cracks (silt and clay) show that an area was once wet and then became dry.
Metamorphic Rocks - Metamorphism is the process in which an existing rock is changed by heat and/or pressure. - Heat and pressure can break the bonds that join atoms in minerals, then the atoms can join together differently as new bonds form. This is called recrystallization. - Foliation is an arrangement of minerals in a flat or wavy parallel bands. - Foliated rocks have minerals that flatten or line up and they can look shiny or banded. - Nonfoliated rocks are made up of mainly one type of mineral or if it has not been subjected to high pressure.