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

SHOW HIDE TRANSCRIPT

[MUSIC PLAYING]

Minerals take time to crystallize.

[MUSIC PLAYING]

Around the volcano, molten rock cools at different rates.

[MUSIC PLAYING]

Gaseous lava cools instantly, forming porous pumice.

[MUSIC PLAYING]

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

[MUSIC PLAYING]

On the basalt flood plain, lava cools over days.

[MUSIC PLAYING]

Small crystals grow in the basalt rock.

[MUSIC PLAYING]

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

[MUSIC PLAYING]

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

SHOW HIDE TRANSCRIPT

[GENTLE MUSIC]

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.

[MUSIC PLAYING]

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

SHOW HIDE TRANSCRIPT

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

[MUSIC PLAYING]

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

[MUSIC PLAYING]

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

SHOW HIDE TRANSCRIPT

[MUSIC PLAYING]

Hot water is a medium for the formation of minerals.

[MUSIC PLAYING]

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

[MUSIC PLAYING]

In many hydrothermal environments, water is heated by magma.

[MUSIC PLAYING]

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

[MUSIC PLAYING]

Colder water moves in to replace it, triggering circulation.

[MUSIC PLAYING]

Water transports dissolved materials into cracks and pockets.

[MUSIC PLAYING]

As enriched water cools, minerals crystallize.

[MUSIC PLAYING]

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

[MUSIC PLAYING]

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

SHOW HIDE TRANSCRIPT

[MUSIC PLAYING]

Rain falls and seeps into the ground.

[MUSIC PLAYING]

Rainwater is slightly acidic.

[MUSIC PLAYING]

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

[MUSIC PLAYING]

The

Leach water continues to descend.

[MUSIC PLAYING]

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

[MUSIC PLAYING]

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

[MUSIC PLAYING]

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

[MUSIC PLAYING]

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

[MUSIC PLAYING]

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.

Credits

You might also like...

Meet six rocks that travelled to the Museum from places like Mexico, Scotland, and even outer space.

Find out what causes volcanoes to erupt and how scientists study them.

Create your own crystals with sugar. Then enjoy your tasty treat!
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