1. Recrystallization:
* Heat: The heat causes the individual mineral grains within the sandstone, primarily quartz, to become more mobile. This allows them to rearrange and grow larger.
* Pressure: The pressure pushes the grains closer together, increasing their contact points and promoting further recrystallization.
2. Cementation:
* Heat: The heat can also cause the dissolution of some minerals, like calcite or silica, within the sandstone. These dissolved minerals then reprecipitate in the spaces between the grains, acting as a cementing agent.
* Pressure: The pressure helps drive the dissolved minerals into the pores, further cementing the grains together.
3. Metamorphism:
* Increasing Heat and Pressure: As the heat and pressure intensify, the sandstone starts to transform into a metamorphic rock.
* Types of Metamorphic Rocks: Depending on the degree of heat and pressure, sandstone can morph into different metamorphic rocks:
* Quartzite: A very hard, dense rock formed when sandstone is subjected to high temperatures and pressures. It's almost entirely made up of quartz.
* Slate: Formed when sandstone is metamorphosed under lower temperatures and pressures. It's characterized by its fine-grained texture and ability to split into thin layers.
* Schist: A metamorphic rock with a more complex mineral composition and a distinct foliated (layered) structure.
4. Other Changes:
* Color Changes: The heat can cause changes in the color of the sandstone, often leading to a more reddish or brown hue.
* Texture Changes: The texture of the sandstone will become finer and more compact as the grains are pressed together and cemented.
In summary: The combined action of heat and pressure on sandstone results in a complex process of recrystallization, cementation, and potentially, metamorphism. This transformation leads to the formation of different metamorphic rocks with unique properties, demonstrating the power of geological forces to reshape the Earth's crust.
