Types of Rocks

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Rock Noun

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[rok]

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Rock

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A naturally occurring solid mixture of one or more minerals or organic matter, forming part of the Earth's crust.

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Example: This image shows eight different types of rocks, illustrating that rocks can vary greatly in color, texture, and composition.

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Mineral Noun

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[min-er-uhl]

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Mineral

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A naturally occurring, inorganic solid with a definite chemical composition and an orderly internal atomic structure.

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Example: This image shows a quartz crystal, an example of a mineral, which is a naturally occurring solid with a specific chemical makeup and an orderly internal structure.

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Composition Noun

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[kom-puh-zish-uhn]

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Composition

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The chemical makeup of a rock, describing the specific minerals or other materials that it contains within its structure.

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Example: A rock's composition is the set of minerals it is made of; for example, granite is composed of quartz, feldspar, and other minerals.

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Texture Noun

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[teks-cher]

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Texture

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The size, shape, and arrangement of the grains or crystals that constitute a rock's physical feel and appearance.

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Example: This image shows the texture of a rock, which is the size, shape, and arrangement of its mineral grains. The visible, interlocking crystals and the 1 cm scale bar show a coarse-grained texture.

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Igneous Rock Noun

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[ig-nee-uhs rok]

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Igneous Rock

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A type of rock that forms from the cooling and solidification of hot, molten rock known as magma or lava.

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Example: Igneous rocks are formed when hot, molten rock (magma or lava) from a volcano cools and solidifies.

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Sedimentary Rock Noun

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[sed-uh-men-tuh-ree rok]

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Sedimentary Rock

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A type of rock formed by the accumulation, compaction, and cementation of mineral or organic particles called sediments.

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Example: This image shows a piece of sandstone, a type of sedimentary rock, highlighting its key features like horizontal layers (bedding) and its composition of grains.

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Metamorphic Rock Noun

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[met-uh-mawr-fik rok]

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Metamorphic Rock

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A type of rock that has been transformed by extreme heat, pressure, or chemical processes without melting completely.

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Example: This image shows how a parent rock like shale transforms into different metamorphic rocks (slate, phyllite, schist, gneiss) with increasing heat and pressure (metamorphism).

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Rock Cycle Noun

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[rok sy-kuhl]

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Rock Cycle

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The continuous series of processes through which rocks are created, transformed from one type to another, and recycled.

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Example: This diagram shows the rock cycle, where magma cools into igneous rock, which weathers into sediment, then compacts into sedimentary rock, and can become metamorphic rock through heat and pressure.

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Magma Noun

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[mag-muh]

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Magma

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Hot, molten rock material that is located beneath the Earth's surface and contains dissolved gases and suspended crystals.

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Example: This diagram shows magma, which is molten rock, located beneath the Earth's oceanic crust at a divergent boundary where tectonic plates are moving apart.

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Lava Noun

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[lah-vuh]

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Lava

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Molten rock that has been expelled from the interior of a terrestrial planet during an eruption or volcanic event.

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Example: This image shows lava, which is molten rock, flowing from eruptive vents on a volcano. The labels point out different features of the flow.