Rock Notes, chap 4
- minerals are naturally occurring, inorganic solids with a definite chemical composition and a crystal structure.
- rocks are made of minerals.
- rocks are mixtures of one or more minerals , rock fragments, volcanic glass, organic matter, or other natural materials.
- rock cycle-process where rocks slowly change from one form to another through time. Any type of rock can change into any other type of rock.
- erode-means to wear down
- 3 types of rocks are igneous, metamorphic, and sedimentary
- principle of conservation of matter-no matter is ever created or destroyed, it is just changed from one form into another.
- any type of rock can be changed into any other type of rock or even into another rock of the same type.
- James Hutton, a Scottish scientist, in 1788, came up with the idea of the rock cycle.
- sedimentary rock is made up of fragments of other rocks that have been broken down by weathering.
- metamorphic rock is made from rocks that have been heated and squeezed by the tremendous pressure inside the Earth.
- igneous rock is formed when any type of rock gets melted by the incredible heat inside the Earth.
Igneous Rocks:
- igneous rocks are formed when magma or lava cools and hardens.
- magma that reaches the Earth’s surface is called lava
- intrusive-igneous rocks that form from magma below the surface of the Earth. They form “IN” the Earth-Intrusive.
- intrusive rocks have larger grains because the magma cools very slowly. The slower the cooling, the larger the grains
- grains and crystals are the same thing
- extrusive-extrusive rocks are formed from lava cooling on the surface of the Earth. Extrusive rocks cool quickly causing small grains. The faster the cooling process, the smaller the grains.
- volcanic glass, such as pumice, obsidian, and scoria cooled so fast that they don’t have grains or crystals.
- basalitic igneous rocks are dense, dark colored rocks
- granitic igneous rocks are less dense, light colored rocks
- basalt and granite are igneous rocks
Metamorphic Rocks:
- metamorphic rocks are rocks that have been changed by heat and pressure.
- metamorphic rocks can be formed from igneous, sedimentary, or other metamorphic rocks.
- high temperatures inside the Earth cause the rocks to soften without actually melting.
- foliated rocks have their grains (crystals) arranged in layers. (think “folded” like towels)
- slate and gneiss are foliated metamorphic rocks
- nonfoliated rocks do not have layers. Quartzite and marble are nonfoliated metamorphic rocks.
Sedimentary Rocks:
- sediments are loose materials such as rock fragments, mineral grains, and bits of shell that have been moved by wind, water, ice, or gravity.
- sedimentary rocks are formed when sediments are pressed and cemented together or when crystals form from solutions.
- compaction and cementation-on your rock cycle drawings, this is what forms the sediment into sedimentary rocks. The tiny particles are pressed together and then cemented by minerals.
- sedimentary rocks often form as layers. The oldest layers are on the bottom and the newest layers are on the top
- fossils are ONLY found in sedimentary rocks
- weathering and erosion cause the formation of sedimentary rocks. Weathering is the breaking down of rocks into smaller pieces by wind, water, and gravity.
- erosion is the carrying away of these small pieces of rock.
- compaction forms sedimentary rocks when the tiny pieces of sediment are pressed together into new rock
- cementation forms sedimentary rocks when water and dissolved chemicals actually cement or glue the tiny pieces of sediment together.
- clastic sedimentary rocks are cemented together
- sandstone and shale are sedimentary rocks
- chemical sedimentary rocks are formed when dissolved chemicals in solutions, such as seawater, form rocks such as halite and gypsum.
- organic sedimentary rocks are made of the remains of once-living things, usually shell fish such as clams, corals, and snails. Limestone is an example of organic sedimentary rock.
- coal is an organic sedimentary rock formed from the remains of dead plants that have been chemically changed and cemented together.