Volcano Review What is this Volcano?
Overview of the Rock Cycle • The rock cycle describes Earth’s natural process of recycling rocks and sediments. • All the rocks on Earth fall into the three distinct categories of sedimentary, igneous, or metamorphic rocks. • The names of these rock types refer to the way the rocks were formed
IgneousRocks • Igneous rocks are formed from magma, the molten form of Earth’s mantle layer. • These rocks can form above ground when lava comes out of a volcano, or they may form under the Earth’s surface when magma cools. • When igneous rocks are broken down chemically and physically the pieces of this rock may become solid rock, creating sedimentary rock. Or, if these rocks undergo heat and pressure they may turn into metamorphic rock. • Granite is a common igneous rock that is formed under the Earth’s surface. • About 75% of the Earth’s crust is granite.
Sedimentary Rocks • Sedimentary rocks form from weathered pieces of other rocks (metamorphic, igneous, or other sedimentary rocks) or from weathered shells of sea creatures. • Also, sedimentary rocks can be precipitated directly out of water as is the case with limestone. • Coal is also an example of a sedimentary rock. • Coal forms when dead organic matter is squeezed together before the material can be decayed. Whatever the case, these rocks must be squeezed and cemented together.
Metamorphic Rocks • Metamorphic rocks form under intense heat and pressure. • These rocks may start out as igneous, sedimentary or another type of metamorphic rock, but due to heat and pressure the characteristics change, generating a metamorphic rock. • It is important to know that rocks continue to change form. What was once a sedimentary rock may become a metamorphic rock when subjected to extreme heat and pressure. • With sufficient time and weathering, that metamorphic rock can become a sedimentary rock once again. Evidence of deformation and stress is often associated with metamorphic rocks due to the fact that they were subject to extreme heat and pressure. • One very common metamorphic rock, is marble. Marble is formed when heat and pressure are applied to limestone for many thousands of years.