How and Where Do Minerals Form?

Did you know that there are more than 5,000 different kinds of minerals on Earth?

Long, green crystal
vivid green, lumpy mineral
Yellow orange cube mineral in white chunky mineral
blue green smooth faceted mineral
Dark orange nubby mineral

WHERE DO THEY COME FROM?

Some form deep underground, while some form on the surface. Some form in just seconds, while others take thousands or millions of years to form. One thing all minerals have in common is that they come from nature. Minerals can form anywhere. 

Explore these five types of environments: Igneous, pegmatitic, metamorphic, hydrothermal, and weathering. How do they produce Earth's amazing variety of minerals?

Igneous Environments

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Minerals take time to crystallize.

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Around the volcano, molten rock cools at different rates.

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Gaseous lava cools instantly, forming porous pumice.

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There's no time for crystals to form, so pumice isn't a mineral.

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On the basalt flood plain, lava cools over days.

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Small crystals grow in the basalt rock.

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Underground, magma cools over millions of years, so crystals in granite grow larger.

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Igneous rocks, and the minerals they contain, form when magma cools and hardens. They can form on or near Earth's surface, or deeper in Earth's crust.

Pegmatitic Environments

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Pegmatites grow in leftover magma after granite forms. H2O is concentrated in the leftover magma. Crystals form on the wall. A few crystals grow large, using up materials in the magma. Different crystals form from the remaining ingredients.

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Pegmatites are a special kind of igneous rock characterized by large— occasionally enormous—interlocking crystals. They form where abundant water and certain chemical elements are present in a crystal.

Metamorphic
Environments

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Mountain chains are thickened sections of Earth's crust piled up by the collision of tectonic plates.

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Within mountains, the weight from overlying rock generates heat and pressure, causing the texture and mineralogy of rocks to change.

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Different minerals form at different

Metamorphic rocks had previous “lives.” The minerals in the original rock formed under one set of conditions. Then, after being subjected to different degrees of heat, pressure, and abundance of water, they transformed into different minerals.

Hydrothermal Environments

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Hot water is a medium for the formation of minerals.

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Water fills tiny cracks and pores in rocks that make up Earth's crust.

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In many hydrothermal environments, water is heated by magma.

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As the water heats up, it rises through cracks in the rocks.

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Colder water moves in to replace it, triggering circulation.

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Water transports dissolved materials into cracks and pockets.

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As enriched water cools, minerals crystallize.

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Over time, the chemical composition of the water changes and different minerals form.

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Hydrothermal minerals form when water, heated by magma, circulates through cracks in rock. The water transports dissolved minerals, which crystallize into minerals in the cracks and small cavities as the water cools.

Weathering Environments

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Rain falls and seeps into the ground.

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Rainwater is slightly acidic.

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As water descends, it strips metals and other elements from soil and rocks, leaving behind a leached zone.

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Leach water continues to descend.

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It reacts with sulfides to form an oxidized zone of colorful minerals.

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Below the water table, water fills tiny pores in rock.

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In this zone, the leach water reacts with sulfides to produce enriched sulfides, dense deposits of metal ores.

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In the primary sulfide zone, beyond the reach of the leach water, minerals remain unchanged.

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Rocks are changed when they are exposed to air, water, and ice at Earth's surface. Weathering is often accompanied by erosion—the transportation of weathered materials by flowing water, wind, ice, and gravity. 

Click on a mineral to learn where it was found.

Image credits

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Image Credits:

elbaite var watermelon, malachite with azurite, fluorite-calcite, fluorite, grossular w calcite and diopside (no credit), microcline with smoky quartz and topaz, microcline var. amazonite, elbaite (red), staurolite in muschovite schist, siderite with quartz, andradite with galena, diopside, dioptase, Denis Finnin/© AMNH; augite, orthoclase, quartz, chalcopyrite, sodalite, muscovite with microcline quartz, elbaite (green), fluorapatite with zinnwaldite, calcite with quartz var. amethyst, fluorite, epidote, fluorapophyllite, malachite, adamite, wulfenite, limonite, halite, Matt Shanley/© AMNH