|The Three Types of Rock|
are three main types of rock. They are sedimentary, igneous, and
metamorphic. There is so much to learn about these three types of rock!
Igneous means "fire made". It forms when melted rock or lava hardens. It forms inside (intrusive) and outside (extrusive) .Extrusive igneous rock cools and hardens outside of the Earth's surface. This is the kind of rock that forms from volcanoes. Intrusive igneous rock forms when magma is trapped inside the Earth. This kind of igneous rock cools very slowly. Granite is intrusive igneous rock. Igneous rocks have a glossy shine. They have a smooth feel and look and feel like colored glass.
Metamorphic rocks are formed under the surface of the Earth from the change that happens due to intense heat and pressure. They have ribbon like layers and may have shiny crystals. Marble is sedimentary rock that has has "morphed" from limestone into metamorphic rock. Igneous and sedimentary rock often change into metamorphic rock. Metamorphic means "change of form". There are two types of metamorphic rock. The two types are Foliates and non-foliates. Foliates are full of mica and chlorite. Non-foliates have no cleavage. Quartzite and marble are non-foliates.
Sedimentary rocks are formed when sand, pebbles, and other sediment gather. Sedimentary rock often have fossils in them. Seventy percent of the Earth is covered with water so sedimentary rocks are the most common rocks all over the world. Sedimentary rocks can form two different ways: pressure- As layer after layer of sediments are deposited the lower layers are pressed tightly under the weight of the layers above. Cementing- some sediments are glued together by minerals in water. Some examples of sedimentary rocks are: limestone, conglomerate, sandstone, and shale. Sandstone is formed from grains of sand pressed tightly together. Sandstone is a very common rock. It is formed from the sand on beaches, in riverbeds, and sand dunes. Sandstone is usually made of the mineral quartz. Limestone is from tiny pieces of shells of dead sea animals which has been cemented together. Conglomerate contains sand and rounded pebbles that have also been cemented together. Shale is formed from mud or clay that has pressed together and is formed in quiet waters like swamps or bogs. Sedimentary rocks are easy to identify because you can actually see the layers.
There is a lot to learn about these types of rock.