Q:

Which igneous rocks are coarse grained due to slow cooling?

A:

Granite and basalt are excellent examples of coarsely grained igneous rocks. The coarseness of such igneous rocks is a result of magma becoming trapped beneath sediment and stone, which allows the liquid to cool at a slower rate.

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Rocks that originate by this slow process are classified as phaneritic. These contrast with aphanitic igneous, which are made up of microscopic grains, and igneous rock that is cooled so quickly it takes on characteristics of glass. The conditions necessary to form phaneritic rock leave it buried beneath the Earth's crust. Over time, wind and water work to erode the mineral material containing this slow-cooled magma, until finally it is exposed to the surface.

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  • Q:

    What are characteristics of igneous rocks?

    A:

    Igneous rocks are formed when melted lava or magma cools and crystallizes, and their unique traits are based on this process. They are strong because their mineral grains grow together tightly as they cool, and their minerals are usually black, white, or gray. They have a texture similar to something baked in an oven, like black bread or peanut brittle.

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  • Q:

    How do igneous rocks form?

    A:

    Igneous rocks are formed when magma crystallizes and solidifies. After this transition from liquid to solid, igneous rocks are classified as either intrusive or extrusive.

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  • Q:

    What are some uses of igneous rocks?

    A:

    Some uses of igneous rock include serving as material for buildings and roads. Igneous rocks reduced to gravel size serve as ballast for railroad beds. Igneous rocks are also used for countertops, backsplashes and sinks. They can be carved into works of art and weapons.

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  • Q:

    Why do igneous rocks not contain fossils?

    A:

    Igneous rocks rarely contain fossils because the formation of a fossil requires sedimentation. A fossil results when the remains of a plant or animal are covered by sediment that hardens, forming the mold that eventually fills with minerals. Igneous rocks form under heat and pressure that destroy organic remnants.

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