How to identify what kind of rock it is, find how rocks are made, and what they are used for. Igneous rocks are formed when lava or magma hardens and cools. Sedimentary rocks form by the compaction and cementation of sediments. Metamorphic rocks form when heat and pressure are exerted on a rock to morph, and bend it. Igneous rocks are formed when hardening magma/lava cools. If they cool extremely quickly, they may have air bubbles If they cool quickly they usually do not have visible crystals But, if they cool slowly over time, then they may have them. Intrusive igneous rocks are rocks that have hardened beneath the Earths surface. Extrusive igneous rocks are rocks that have hardened and solidified above ground. Typically, rocks that harden intrusively have more time to solidify than extrusive rocks. Because it is in the crust, it is hotter, so that slows down the cooling. Scoria Andesite Coarse-grained granite Obsidian Basalt Diorite Pegmatite Sedimentary rocks form when sediments, like sand or dirt, get cemented together over a long period of time. When there are large pieces pressed together to form a rock, then it is called a conglomerate, sedimentary rock Breccia Chert Halite LimestoneShale Sandstone The grain of the mineral/rock is how rough it is. Sandstone has a fairly small, but visible, grain. While limestone has no visible grain to the naked eye. Metamorphic rocks Metamorphic rocks happen when a rock(sedimentary or igneous) is in a place with a lot of heat and a lot of pressure. The rock is constantly under pressure and is heated up to the point where it is on the brink of melting, allowing the rock to be bent and twisted into a new rock. When shale is morphed it turns into slate. Shale (sedimentary) Pressure Heat Slate (metamorphic) Thousands to millions of years Metamorphic rock characteristics Some metamorphic rocks have a layered or banded appearance to them, and some may not. Gneiss has a layered pattern. While slate does not. Contact metamorphism and foliation Contact metamorphism is the alteration of a rock, mainly by heat, which occurs adjacent to a dike, sill, magma chamber, or other magma body. If a metamorphic rock is foliated, it means that it has a banding or layered pattern that is the result of exposure to heat and direct pressure. Sources: Metamorphic rocks What they are, (and what they were) Marble(was limestone) Quartzite(was sandstone) Hornfels(Hornfels is a generic name for contact metamorphic rocks that are non-foliated and too fine-grained to allow ready mineral identification) Slate(was shale) Gneiss(was granular mineral grains of abundant quartz or feldspar) Minerals are when only one thing is used to create it. Pure quartz (This is Rose Quartz) is a mineral. Rocks are when several minerals come together to form it. This is quartz-diorite. It can contain feldspar, pyroxene, hornblend and quartz One of the most popular uses for minerals is jewelry. Commonly you will find minerals like topaz, citrine, and emerald in rings and necklaces But some minerals are used for other things. Diamonds can be used to put on saw blades because of their hardness. On Mohs scale it is a ten. The only problem is that diamonds are scarce, hence the expensive prices. These saw blades have very small diamonds on the edges so it can cut through things like marble. As stated before, when an igneous rock slowly cools it has more crystals. Usually the crystals are quartz mica or feldspar. When a rock evenly breaks along 90 degree angles this is called cleavage. Mica has perfect cleavage and comes off in sheets. Fracture is when a rock breaks along uneven angles This is a single sheet of mica Quartz-diorite is fractured Location Some rocks/minerals can be found in specific areas, not just in peoples backyards. Diamonds are a good example. The only diamond mine in the U.S that is open to the public is in Arkansas. There are people who are looking for diamonds in Africa because of its unexcavated land. This scoria is commonly found in Texas