| Themes > Science > Earth Sciences > Geology > Rocks and Minerals > Form Solid Mineral Deposits |
Some minerals, given time and circumstance, form solid deposits. These solid mineral deposits are known as rock. Pressure, temperature, erosion, and friction are forces that effect the formation of rocks. The rock formation process allows geologists to classify rocks into three groups: sedimentary, igneous, and metamorphic. Sedimentary rock forms when layers of "sediment" (small particles of solid minerals like sand and pebbles) fuse together over time under the force of water or wind. Sedimentary rock is commonly found in and near riverbeds and streambeds. Igneous ("fire-formed") rock forms after minerals are heated to extremely high temperatures and then allowed to cool. Hawaii is a well-known source of igneous rock. Most igneous rock forms when hot molten lava cools to a solid state. Metamorphic rock forms when rock undergoes a transformation from one structure to another, usually caused by pressure, heat, and water. For example, a rock that is compacted to a more crystalline condition has undergone a metamorphosis. |
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