Rocks Recycling the Earth
The Rock Cycle • Have you ever looked at a rock and wondered how it got there? Have you ever wondered what rocks are made of? • http://www.schooltube.com/video/503ca205aae459f47494/The-Rock-Cycle
Three types of rock • Igneous rock – formed by volcanoes – lava cooling on the surface of the Earth. • Metamorphic rock – rock changed by high pressure and temperature deep underground. • Sedimentary rock – weathered mineral grains that become bound together due to compaction.
What is a rock? • A rock is a mixture of minerals. These minerals are mixed throughout time. Imagine a chocolate chip cookie. Think about what you would need to do to make a cookie. You would take your ingredients – the eggs, chips, sugar, salt, flour, milk and other stuff and put it in a bowl and stir it together. The same thing happens deep inside the Earth with various minerals being the batter of our rock cookies.
What is the rock cycle? • Most rocks start out life as a liquid deep within the Earth in the mantle (the middle layer of our Earth between the core and crust). This magma (lava beneath the surface of the Earth is called magma) is the beginning stage of a rock.
Igneous rocks When magma makes its way to the surface of the Earth it is called a volcano. The liquid rock that spews out is known as lava. When the lava cools on the surface it produces igneous rock.
Intrusive igneous rock • Magma is made up of atoms and molecules of melted minerals. As magma cools, the atoms and molecules rearrange themselves into new crystals called mineral grains. Rocks form as the mineral grains grow together. Rocks that form from magma below the surface are called intrusive igneous rocks. These rocks form slowly resulting in large grained rocks. Intrusive rocks are found at the surface only after the soil and rock coverings have been removed in a process called erosion.
Extrusive igneous rock • Extrusive igneous rocks are formed as lava cools on the surface of the Earth. When lava flows on the surface of the Earth, it is exposed to air and water. Under these conditions the lava cools quickly forming basaltic lava. The quick cooling rate keeps the mineral grains from growing large. Extrusive igneous rocks are fine grained.
Volcanic glass • Pumice, obsidian, and scoria are all examples of volcanic glass. These rocks cooled quickly and are fine grained. Sometimes gasses get trapped inside of the cooling lava forming pockets.
Classifying igneous rocks • Basaltic rocks • -dense dark-colored rocks • -form from magma rich in magnesium and iron • -found in places such as Hawaii
Classifying igneous rocks • Granitic rocks • -light-colored rocks less dense than basalt • -form from magma less rich in magnesium and iron, but containing silica • -released explosively from volcanoes because of trapped gasses
Classifying igneous rocks • Andesitic rocks • -mineral composition in-between basaltic and granitic • -released explosively from volcanoes because of trapped gasses • -found around the rim of the Pacific Ocean
Metamorphic rock • Rocks that are changed because of temperature and pressure or hot fluids are metamorphic rocks. • Changes can be in the form of the rock, the composition of the rock or both. • Rocks beneath the surface of the Earth can be exposed to high pressures and temperatures leading to melting or flattening.
Classifying metamorphic rocks • Foliated rocks have mineral grains that are flattened and lined up parallel. • Examples of these types of rock are gneiss and slate. Slate forms from shale -a sedimentary rock. Gneiss is changed granite.
Classifying metamorphic rocks • Non-foliated rocks do not have any layering. The grains grow and rearrange but do not form layers. • An example of this types of rock is quartzite which is formed from sandstone which is heated under pressure. Another example of this is marble which is formed from the sedimentary rock limestone.
Sedimentary rocks • To be continued…