THE ROCK CYCLE

How Rocks are Formed Rocks are made of two or more different minerals produced in a variety of ways and cycled many times. This is called the rock cycle.

How are igneous rocks formed? Igneous rocks are called fire rocks. Intrusive igneous rock is formed within the earth when magma becomes trapped in pockets and then cools slowly. Ex. Talkeetna Mtns. Extrusive igneous rock is formed when volcanoes erupt and lava rapidly cools above ground.

Granite rocks are intrusive igneous rocks which were formed by slowly cooling pockets of magma that were trapped beneath the earth's surface. Granite is used for long lasting monuments and for trim and decoration on buildings. Pumice rocks are extrusive igneous rocks which were formed when lava cooled quickly above ground. You can see where little pockets of air had been. This rock is so light, that many pumice rocks will actually float in water. Pumice is actually a kind of glass and not a mixture of minerals. Because this rock is so light, it is used quite often as a decorative landscape stone. Ground to a powder, it is used as an abrasive in polish compounds and in Lava© soap. Obsidian rocks are igneous rocks that form when lava cools quickly above ground. Obsidian is actually glass and not a mixture of minerals. The edges of this rock are very sharp.

How are sedimentary rocks formed? Over long periods of time little pieces of rock are eroded by wind and water. These little pieces are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer is deposited on top of each other. These layers are pressed down over time, until the bottom layers slowly turn into sedimentary rock.

Sandstone rocks are sedimentary rocks made from small grains of the minerals quartz and feldspar. They often form in layers as seen in this picture. They are often used as building stones. Limestone rocks are sedimentary rocks that are made from the mineral calcite which came from the beds of evaporated seas and lakes and from sea animal shells. This rock is used in concrete and is an excellent building stone for humid regions. Shale rock is a type of sedimentary rock formed from clay that is compacted together by pressure. They are used to make bricks and other material that is fired in a kiln.

How are metamorphic rocks formed? Metamorphic rocks are rocks that have "morphed" or changed into another kind of rock. were once igneous or sedimentary rocks. formed under tons of pressure which causes heat to build up, causing them to change form.

Schist rocks are metamorphic Schist rocks are metamorphic. These rocks can be formed from basalt, an igneous rock; shale, a sedimentary rock; or slate, a metamorphic rock. Through tremendous heat and pressure, these rocks were transformed into this new kind of rock. Gneiss rocks are metamorphic. These rocks may have been granite, which is an igneous rock, but heat and pressure changed it. You can see how the mineral grains in the rock were flattened through tremendous heat and pressure and are arranged in alternating patterns.

Internet Activity

Layers of the Earth Have you ever wondered what it is made of? Cantalope Analogy

Layers Crust Lithosphere Mantle Outer Core Inner Core

Crust The outermost layer of the earth consisting of moving plates floating on top of the liquid hot upper mantle (molten rock). It is composed mainly of basalt and granite and is part of the lithosphere.

Lithosphere Greek for "rocky" sphere. It is the solid outermost shell of the Earth. It includes the crust and the uppermost layer of the mantle which is joined to the crust. The lithosphere is broken up into different plates.

Lithospheric Plates Hard plates that float and move on top of the liquid molten magma of the mantle.

Mantle Hot liquid layer below the crust, has currents that are driven by convection (hotter magma rises cooler magma sinks).

Outer Core The liquid outer core surrounds the inner core and is believed to be composed of iron mixed with nickel and trace amounts of lighter elements.

Inner Core The deepest innermost layer composed mainly of a nickel is very hot. It is under so much pressure that it is solid. It has a radius of about 1,220 km and is located from 5,100 to 6,300 km below earth's surface and can be as hot as 6000 C.

Internet Resources Science Monster Layers of Earth Video Clip – 9 min.