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Some facts about igneous rocks include that they are glassy in nature, that pumice igneous rock is the lightest type of rock on Earth, and that the moon is made of igneous rocks. Igneous rocks come from molten magma and ... More »

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Sedimentary rocks are rocks made by sediment that has accumulated over millions of years. This sediment can accumulate on the surface of the Earth or under water. Sedimentary rocks tend to resemble the sediment that crea... More »

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The specific type of rock that forms when magma cools at the Earth's surface is extrusive igneous rock. Igneous rock forms when magma cools, but where the magma cools determines the type of igneous rock that forms. Igneo... More »

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A fine-grained igneous rock is a rock that is formed by melted magma cooling so quickly at the surface of the Earth that only tiny crystals form, most too small to be seen with the naked eye. Basalt is an example of such... More »

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Gabbro, a type of intrusive igneous rock, is formed when magma cools and solidifies inside the crust of the Earth. Because it cools slowly, it is coarsely grained. More »

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Mafic, or basaltic, igneous rocks contain a greater portion of iron and magnesium than silica, and they are often much darker in color, typically black, dark brown or dark gray, compared to the lighter-colored igneous ro... More »

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Porphyritic rock is a texture of igneous rock with two distinctly different crystal sizes due to two periods of cooling occurring at different rates. Larger crystals are called phenocrysts, while the smaller grains are k... More »

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