The rock cycle illustrates the process that creates and changes rocks. The rock cycle shows the three types of rock- igneous, metamorphic, and sedimentary- and the processes that form them.
How are rocks classified? Based on the way the rock was formed
Three types of Rocks Sedimentary Igneous Metamorphic
What are sedimentary rocks? Rocks made of sediments What are sediments? Pieces of rocks, shells, plants, or animals. Sedimentary rock make up 75% of rocks on the earth’s surface
How are sedimentary rocks formed? Compaction- Sediments deposited and lower levels pressed together Cementation- Minerals dissolved in water cement sediments together
Major Characteristics of Sedimentary Rocks Formed in layers Usually formed in water Only rocks with fossils
How are sedimentary rocks grouped? Grouped by grain size or composition Clastic- Made of broken pieces of rock
Conglomerate- Large, rounded rocks cemented together Breccia- Sharp, angular pieces cemented together
Sedimentary rocks are grouped into three groups Sandstone Organic Rocks Chemical Rocks
Group 1- Sandstone Made from sand-sized granules Examples are shale and siltstone Group 2- Organic rocks Made directly or indirectly from living material Examples are limestone (shells pressed together) or coal (plants pressed together) Group 3- Chemical rocks Water evaporates leaving a chemical deposit Example is gypsum
What are Igneous rocks? Rocks that are formed from cooling lava How are igneous rocks formed? Formed from cooling magma or lava Also known as fire rock
Types of igneous rocks Intrusive Formed from magma within the earth The crystals that form the rock are large because they take a long time to cool Extrusive Formed from lava outside the earth The crystals are small because they cool so fast
Composition The color of the rock is due to its composition (the types of minerals that make up the rock) Quartz- white Feldspar- pink Mica- dark Olivine- dark green Amphibole- dark Pyroxene- dark
Common Igneous rocks Granite Forms the continental crust Most common coarse grained rock Used in construction of homes (countertops) Basalt Beneath the ocean floor Most common fine grained rock Make-up volcanic islands Andesite Cooling rate has changed, so the rock has crystals of different sizes
Scoria Same chemical composition as basalt 50% holes- from trapped gases Pumice Natural glass- crystals cooled quickly Many holes so it is able to float
What are metamorphic rocks? Rocks which have changed form. What is metamorphism? Changing of a rock into a different rock by heat, pressure, or chemical reaction. Types of metamorphism Contact metamorphism- Magma heats the rocks around it Regional metamorphism- Areas buried deep within the earth
Types of Metamorphic rock Foliated Mineral crystals arranged in parallel layers or bands Tend to break along these bands Examples Slate- a fine grained rock made from shale Schist- a medium grained rock made from slate, basalt, granite Gneiss- a fine grained rock made from granite
Unfoliated No bands Examples Quartzite- medium grained rock from sandstone Marble- coarse grained rock from limestone