Here's how it works:
1. Crystallization: As magma cools, minerals start to crystallize out of the melt.
2. Early Crystallization: The minerals that crystallize first are typically those with the highest melting points.
3. Density Difference: The early-formed crystals often have a different density than the remaining magma.
4. Separation: This density difference can cause the crystals to settle to the bottom (if they are denser) or float to the top (if they are less dense).
5. Magma Composition Change: The removal of these early-formed crystals changes the chemical composition of the remaining magma. This process is called fractional crystallization.
Example:
Imagine a magma chamber with a high concentration of silica. As the magma cools, olivine crystals (rich in iron and magnesium) will be the first to form. These crystals are denser than the remaining magma and sink to the bottom. This process removes iron and magnesium from the magma, leading to the formation of a more silica-rich magma that can eventually crystallize into granite.
