How Do Minerals Form?
How minerals form depends chiefly on physical and chemical conditions in their source environments.
Hydrothermal Environments
Even in the driest places on Earth, water is involved in forming minerals.
Hydrothermal processes require hot water, which dissolves minerals and transports their components where the water goes, along fractures and through porous rocks.
As the water travels, it cools—or other conditions change—and the dissolved materials can be deposited in spaces in the surrounding rocks, forming veins or pockets of minerals.
Metamorphic Environments
Metamorphic rocks all had previous “lives.”
The minerals in the original rock were formed at one set of conditions, but were then subjected to different conditions of heat, pressure, and H2O abundance in Earth’s crust.
They responded to that change by transforming to become minerals stable under the new conditions. Metamorphic rocks and minerals record the history of the dynamic Earth.
Igneous Environments
Igneous rocks and minerals solidify from molten rock, called magma below the Earth’s crust and lava when flowing above ground.
These rocks and their mineral components, presented below, are the result of processes that formed Earth and other rocky planets. Igneous environments are integral to the recycling of Earth’s crust; they produce the granite roots of the continental plates and basaltic rocks beneath the oceans. For those studying our dynamic planet, igneous rocks and minerals are windows into Earth’s deep processes.
Pegmatitic Environments
Pegmatites are a special kind of igneous rock characterized by large, occasionally enormous, interlocking crystals–sometimes of unusual minerals containing rare elements.
Large crystals typically mean that magma cooled slowly, allowing crystals to grow for a long time, but pegmatites are rule-breakers.
Special circumstances, particularly enrichment in H2O, allow them to solidify rapidly, sometimes in just a few days. Pegmatites are a source of minerals for gemstones, industry, and rare element ores.
Weathering Environments
Earth is always changing. As rocks and minerals become exposed at its surface, the weathering process changes them through exposure to air, water, ice, and life.
Weathering is often accompanied by erosion, or the transportation of weathered materials by flowing water, wind, ice, and gravity.
Weathering counteracts Earth’s dynamic building processes and, over millions of years, has produced the clays, soils, and salts critical to the survival of life on Earth—including our own.