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Rock | A mixture of one or more minerals, rock fragments, volcanic glass, organic matter, or other natural materials; can be igneous, metamorphic, or sedimentary |
Rock cycle | A model that describes how rocks slowly change from one form to another through time |
Lava | Molten rock that flows from volcanoes onto Earth’s surface |
Igneous rock | Rock formed when magma or lava cools and hardens |
Intrusive | Describes a type of igneous rock that generally contains large crystals and forms when magma cools slowly beneath Earth’s surface |
Extrusive | Describes a type of igneous rock that generally contains fine (small) grains and forms when magma cools quickly at or near Earth’s surface |
Basaltic | Describes dense, dark-colored igneous rock formed from magma rich in magnesium and iron and poor in silica |
Granitic | Describes generally light-colored, silica-rich igneous rock that is less dense than basaltic rock |
Metamorphic rock | Rock that forms when heat, pressure, or fluids act on igneous, sedimentary, or other metamorphic rock to change its form or composition, or both |
Foliated | Describes metamorphic rock, such as slate and gneiss, whose mineral grains line up in parallel layers |
Nonfoliated | Describes metamorphic rock, such as quartzite or marble, whose mineral grains grow and rearrange but generally do not form layers |
Sediments | Loose materials, such as rock fragments, mineral grains, and the remains of once-living plants and animals, that have been moved by wind, water, ice, or gravity |
Sedimentary rock | Rock that forms when sediments are compacted and cemented together or when minerals form from solutions |
Compaction | Process that forms sedimentary rocks when layers of sediments are compressed by the weight of the layers above them |
Cementation | Process that forms sedimentary rock when sediment grains are held together by natural cements that are produced when water moves through rock and soil |