Formation of Minerals: Where Do Minerals Come From
Minerals are naturally occurring inorganic solids with a specific chemical composition and a crystal structure. Their formation is a complex process that can occur in various geological environments.
Minerals are all around you. They are used to make your house, your computer, even the buttons on your jeans. But, where do minerals come from? There are many types of minerals, and they do not all form in the same way. Some minerals form when salt water on Earth's surface evaporates. Others form from water mixtures that are seeping through rocks far below your feet. Still others form when mixtures of really hot molten rock cool.Formation from Magma and Lava
There are places inside Earth where rock will melt. Melted rock inside the Earth is also called molten rock, or magma. Magma is a molten mixture of substances that can be hotter than 1,000°C. Magma moves up through Earth's crust, but it does not always reach the surface. When magma erupts onto Earth’s surface, it is known as lava. As lava flows from volcanoes it starts to cool. Minerals form when magma and lava cool.
Example: Olivine and pyroxene in basalt; Quartz and feldspar in granite.
 |
| Formation of Minerals: Where Do Minerals Come From? Mix of minerals. Photo: RoseCreekTreasure |
Minerals from Magma
The magma mixture changes over time as different minerals crystallize out of the magma. A very small amount of water is mixed in with the magma. The last part of the magma to solidify contains more water than the magma that first formed rocks. It also contains rare chemical elements. The minerals formed from this type of magma are often valuable because they have concentrations of rare chemical elements. When magma cools very slowly, very large crystals can grow. These mineral deposits are good sources of crystals that are used to make jewelry. For example, magma can form large topaz crystals.
Minerals from Lava
Formation from Solutions
Hydrothermal Activity
In hydrothermal systems, hot, mineral-rich water moves through cracks and fractures in the Earth’s crust. As the water cools or reacts with surrounding rocks, minerals precipitate and form solid deposits called hydrothermal veins. These veins are rich in minerals such as quartz, gold, silver, and sulfides like galena (lead sulfide) and chalcopyrite (copper-iron sulfide). Hydrothermal processes are crucial in forming many valuable ore deposits.
Cave Formation
In caves, minerals such as calcite (calcium carbonate) can form speleothems like stalactites (hanging from the ceiling) and stalagmites (rising from the floor). These formations occur when mineral-rich water drips into an open space and releases carbon dioxide, causing the dissolved calcium carbonate to precipitate and crystallize over time.
Evaporation: Minerals from Salt Water
When water containing dissolved minerals evaporates, the concentration of these minerals increases. As the water evaporates further, the solution can become supersaturated—meaning it holds more dissolved minerals than it can sustain. At this point, minerals begin to crystallize and form solid deposits. This process commonly occurs in evaporite environments, such as salt flats and playas, where minerals like halite (rock salt), gypsum, and sylvite form.
Both tap water and bottled water contain trace amounts of dissolved minerals, but for significant mineral crystallization to occur, the water needs to contain a high concentration of dissolved salts. This is why seawater and certain inland bodies of water, such as Mono Lake in California or Utah’s Great Salt Lake, can produce mineral deposits. As these waters evaporate, minerals like halite and calcite can precipitate out as solid crystals.
When water evaporates, it leaves behind a solid mineral precipitate because minerals do not evaporate with the water. The amount of minerals left behind matches what was originally dissolved in the water.
Minerals from Hot Underground Water
Hot water can hold more dissolved particles than cold water. The hot, salty solution reacts with the rocks around it and picks up more dissolved particles. As it flows through open spaces in rocks, it deposits solid minerals. The mineral deposits that form when a mineral fills cracks in rocks are called veins.
Alteration of Existing Minerals
When existing rocks are subjected to high pressure, high temperature, or chemically reactive fluids within the Earth's crust, they undergo changes in mineral composition and texture. This process is known as metamorphism, and it results in the formation of new minerals that are stable under the new conditions. For instance, limestone can be transformed into marble (recrystallized calcite), and shale can become slate (recrystallized mica).
Regional Metamorphism
Occurs over large areas during mountain-building processes, where the intense heat and pressure can cause minerals to recrystallize without melting. This process can create new minerals like garnet, kyanite, and staurolite.
Contact Metamorphism
Occurs when rocks are heated by nearby molten magma, leading to the formation of minerals like wollastonite and garnet.
Biological Processes
Biomineralization: Some minerals form as a result of biological activity. Organisms like mollusks, corals, and algae secrete minerals such as calcite and aragonite to build shells and skeletons. Microorganisms can also influence the formation of minerals like pyrite (iron sulfide) through biological processes.
Organic Mineral Precipitation: In some cases, minerals form in association with decaying organic matter, leading to the formation of phosphates (such as apatite) in guano deposits or the accumulation of silica from diatom skeletons in marine sediments.
Weathering Processes
Mechanical and Chemical Weathering: When rocks are broken down by weathering, minerals are released and can be re-deposited elsewhere. For example, feldspar minerals weather to form clay minerals such as kaolinite, and iron-rich minerals can oxidize to form hematite and limonite.
Soil Formation: As rocks weather and break down, they contribute to the mineral content of soil. Secondary minerals like clay minerals, iron oxides, and carbonate minerals form from the alteration of primary minerals present in the parent rock.
Sublimation from Volcanic Gases
In rare cases, minerals can form from the direct deposition of gases emitted by volcanic vents. For example, sulfur crystals can form from the sublimation of sulfur dioxide gas near fumaroles, and other minerals like orpiment (arsenic sulfide) can also form in similar environments.
Key Factors Influencing Mineral Formation
Temperature: Affects the rate of reaction and the type of minerals formed.
Pressure: Influences the stability of minerals; higher pressure can lead to denser mineral structures.
Time: Longer durations allow for larger crystals or more complex mineral assemblages.
Chemical Composition: Determines what minerals can potentially form; the presence of certain elements or compounds is crucial.
Water: Acts as a medium for ion transport in many mineral formation processes.