All rock is one of three types: sedimentary, igneous or metamorphic.
Everyone can see changes in the environment, but the timeline for these changes varies greatly by location. Coasts change quickly; you see daily, monthly and yearly changes in the shape of the coastline. Interior land changes more slowly. A river might flood only once every century, and the growth of mountains is often imperceptible. Near faults and volcanoes, catastrophic events cause instant change to the surrounding landscape.
The Rock Cycle
The rock cycle consists of the processes by which earth changes from one type to another: sedimentary, metamorphic and igneous. Rocks do not just form as one type and stay there; they remain in constant motion. A rock is any "naturally formed, nonliving, firm and coherent aggregate mass of solid matter that constitutes part of a planet," according to the Idaho Museum of Natural History. Rock cycles have no actual beginning, because each type of rock is made from the others in an endless chain.
Sedimentary Rock
When you place moderate amounts of pressure on layers of sediments, they compress to form sedimentary rocks such as sandstone. Sediments are either biological detritus such as bones and plants or pieces of other rocks called clasts. Sedimentary rocks are named for the size of the particles used to make them--such as sandstone from sand, siltstone from silt and mudstone from mud, according to the Idaho Museum of Natural History. For a geologist, gravel means anything with clasts from 1/10 to 1/5 inch in diameter. Conglomerates are made from rounded gravel, and breccia is made of angular or sharp-edged gravel. Limestone forms from organisms that have recrystallized under pressure, but it is still considered stone.
Metamorphic Rock
When you subject sedimentary or igneous rock to extreme heat and pressure, it transforms into metamorphic rock. Meta means change and morph means form, and change-form is exactly what the molten metamorphic rock does. Also called magma or molten rock, it only forms at specific locations, usually near fault lines. When magma cools, it crystallizes just like ice from water, according to Vision Learning.
Igneous Rock
Though all igneous rock forms from metamorphic rock, they form in two very different environments. Extrusive rocks cool quickly on the surface of volcanoes forming basalt. Quick cooling makes the crystals too small to see without a magnifying glass or microscope. Intrusive igneous rocks cool in plutons (cool areas) deep below the Earth's surface. It takes a long time for these rocks to cool, so they have time to grow much larger crystals. Each type of extrusive rock has an intrusive counterpart such as rhyolite and granite or gabbro and basalt, the Idaho Museum of Natural History says.
Timeline
Some rock processes, such as volcanic eruptions and earthquakes, happen instantly. Others, such as rising mountain ranges, happen slowly. Any rock can be pushed up and exposed to weathering and erosion, and similarly, any rock and be pushed down and melted. Therefore, the rock cycle is not a circle, because many paths connect the three states, according to Vision Learning.
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