Rocks
Igneous Rocks
These come from magma Š melted rock inside earth. Lava is magma that flows out onto the earthÕs surface. Crystallization happens when the magma or lava cools down. Rocks made up of different minerals crystallize at different temperatures. Igneous rocks are categorized according to mineral content. Felsic have high silca content and are light colored. Mafic have low silica content, are darker colored and have high amounts of Fe & Mg content. Ultramafic have very low silica content and have very high amounts of Fe & Mg.

Igneous rocks are also categorized by the size of their crystals, which has to do with how long it took to cool and where it cooled. Extrusive rocks are fine-grained igneous rocks that cool quickly on earthÕs surface. These rocks cool too quickly for large sized crystals to form. Intrusive rocks are coarse-grained igneous rocks that cool slowly beneath earthÕs surface. Granite is the most common intrusive igneous rock. Porphyritic rocks are a mixture of large, coarse grains and smaller, fine grains. This indicates that the rock had a complicated cooling history, where some parts cooled faster than others. An intrustions is when magma cuts across other rocks and cools, forming igneous rock inside of another kind of rock.  This cutting across other types of rock is called an intrusion; the magma intrudes on the other rock.

Sedimentary Rocks
Sedimentary rocks come from small pieces that are cemented together. Weathering  is when the surface of earth is worn down and sediments are created. Chemical weathering is when minerals in rock are dissolved.  Physical weathering is when rock fragments break off because of wind, water, gravity, etc.  Weathering produces sediments, the small pieces of rock. 
Erosion then happens, which is the removal and movement of sediments because of wind, moving water, gravity or glaciers. Deposition is the next step, when sediments are laid down or sink to the bottoms of water. This can happen in water.  As moving water slows down the largest particles sink first. There is a characteristic layering, with the largest particles on bottom, smallest on top. Wind can also lay down same layering effect but wind can only move small grains, like a sand dune. Glaciers can also move sediments dumping all the sediments in an unsorted pile. Lithification is the cementing of sediments into rocks. This happens by either compaction where the weight of stuff on top causes sediments to move closer together or cementation where minerals fill in in-between spaces & make minerals stick together. There are several features of sedimentary rocks that you can use to identify sedimentary rocks. Stratification or bedding is horizontal layering caused by sorted sediments that are laid down. Ripple marks are caused by sediment that is moved into small ridges (like sand dunes or sand under water at a beach or river) that gets buried and preserved. Fossils are preserved remains or impressions from living things that got buried and are preserved

There are three types of sedimentary rocks. Clastic rocks are sediments (particles) that are cemented together. These can be fine grained, where the sediments are too small to be seen. Medium grained have larger grains but they still might be hard to see. Coarse grained have sediments you can see.  Chemical sedimentary rocks are dissolved minerals that are left behind when water evaporates or minerals precipitate out of solution. Organic sedimentary rocks are formed from the remains of living things. This can happen when remains get covered, such as shells or when plant remains get covered and cemented into coal.

Metamorphic Rocks
Metamorphic rocks are formed when rocks experience high temperatures from earthÕs internal heat or the rocks experience high pressure (being squeezed) which causes changes in minerals. Vertical pressure is from the weight of rock on top and compressive pressure is by forces during mountain building. Types of metamorphism are low-grade, intermediate-grade, high-grade. The grade just means the degree of heat and pressure the rock experiences. Regional metamorphism is when large areas of land undergo same conditions, producing the same rock (whole east coast of US). Contact metamorphism is when molten rock (magma intrusion) comes in contact with solid rock and heats it, changing it. Hydrothermal metamorphism is when very hot water comes in contact with solid rock. Yellowstone National Park shows this with its volcanoes and underwater hypothermal vents. Metamorphic rocks are categorized by their characteristic of texture. Foliated means there are bands or wavy layers of minerals that are formed. Nonfoliated rocks do not have crystals that form layers.

Rock Cycle is the continuous cycle where rocks change into other rocks. To become a sedimentary rock, a rock has to undergo weathering and erosion. It then is broken up into sediments and then the sediments have to cemented together (lithification). To become an igneous rock, a rock has to be melted and then the magma or lava has to cool. To become a metamorphic rock, a rock has to be put under heat and pressure so that the minerals actually change.