* Heat and Pressure: Metamorphism occurs when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are subjected to intense heat and pressure deep within the Earth's crust.
* Mineral Transformation: These conditions cause the existing minerals in the rock to become unstable. They start to break down and rearrange their atoms into new, more stable mineral structures.
* Grain Growth: As the minerals recrystallize, they often grow larger. This growth can happen in two ways:
* Neocrystallization: New minerals form entirely from the existing mineral material.
* Grain Boundary Migration: Existing mineral grains can grow by consuming smaller neighboring grains.
* Space Reduction: As grains grow larger, the spaces between them often decrease. This is because the larger grains can fill in the gaps previously occupied by smaller grains.
Other factors that can influence grain size and spacing:
* Original Rock Composition: The types of minerals present in the original rock will influence the new minerals formed during metamorphism.
* Fluid Activity: Fluids circulating through the rock can enhance chemical reactions and accelerate recrystallization.
* Duration of Metamorphism: The longer the rock is exposed to heat and pressure, the more time there is for recrystallization to occur, potentially leading to larger grain sizes and reduced spacing.
Examples of Metamorphic Rocks with Different Grain Sizes:
* Slate: A fine-grained metamorphic rock with very small grains and little space between them.
* Schist: A medium-grained metamorphic rock with larger, more easily recognizable grains.
* Gneiss: A coarse-grained metamorphic rock with very large grains and often distinct layering.
So, recrystallization is the key process that changes the space between grains in a metamorphic rock, and this change can significantly influence the rock's texture and properties.
