When a volcano erupts or through cracks on the surface of the earth lava oozes out and cools down to form igneous rocks. Like granite and basalt. Small pieces of rocks are called sediments. And when they get transported by water or wind because of pressure they get compressed or are cemented together and form sedimentary rocks. Like limestone and gypsum and etc etc... When igneous or sedimentary rocks are changed in thier characteristics and form due to high pressure or temperature they form metamorphic rocks. Like marble and slate . : )
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Igneous Rocks Igneous rocks are those that solidify from a molten or partially molten state. These rocks are characterized as either extrusive or intrusive.
Sedimentary Rocks
Erosion and deposition play a key part in the formation of sedimentary rocks. Wind, water, ice, and chemicals break down existing rock into sediment that is then transported and deposited by wind, water, and glaciers. As sediment accumulates with time (thousands of years) it becomes compacted and cemented (lithified), eventually forming rock. Over a period spanning hundreds of millions of years, oceans, rivers, and great deserts covered Utah and deposited the sediment that has lithified into the sedimentary rocks we see today. Some common sedimentary rocks are shale, sand
Metamorphic Rocks
Metamorphic rocks are any rock type that has been altered by heat, pressure, and/or the chemical action of fluids and gases. Metamorphic rocks are classified by their structure and their dominant minerals. Metamorphic rock structure is either foliated (has a definite planar structure) or nonfoliated (massive, without structure). stone, limestone, and conglomerate.  
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