How do minerals form in magmatic, hydrothermal, and metamorphic environments?

• A. Magmatic minerals crystallize from cooling magma.
• B. Hydrothermal minerals crystallize from cooling magma.
• C. Metamorphic minerals recrystallize under heat/pressure in existing rocks.
• D. All minerals form only from surface weathering.

Answer: (C)

In metamorphic settings, minerals form by recrystallizing within existing rocks as they experience higher temperatures and pressures. This process doesn't melt the rock; instead, the mineral grains reassemble into more stable configurations under the new conditions, leading to new mineral assemblages and textures such as the development of larger grains or foliated textures. That is why the statement about metamorphic minerals changing through recrystallization under heat and pressure in already solid rocks is the best description of how minerals form in that environment.

For contrast, minerals formed from cooling magma crystallize as the melt solidifies, giving igneous rocks like quartz, feldspar, and olivine. Minerals from hydrothermal systems form from hot, mineral-rich fluids circulating through rock and precipitating minerals as those fluids change temperature or chemistry, not from cooling magma. And surface weathering is not the sole pathway for mineral formation.