Metamorphic rocks
Note: All pictures are meant as guides only, as often the difference between one metamorphic rock type and another is only in the size of the mineral grains. Metamorphosis is the name of the process a caterpillar undergoes as it changes to a butterfly. Similarly, metamorphism is a part of the rock cycle that occurs when rocks deeply buried in the Earth are heated and compressed sufficiently to change the properties of the rocks, making them harder and more coherent and forming new minerals. When rocks undergo this type of change, they are called metamorphic rocks. Metamorphic changes can be brought about by a combination of heat and high pressure, as is present deep inside the Earth, or may also occur with high temperatures alone, such as in rocks adjacent to lava intrusions. The different types of metamorphic rock formed are determined by temperate, pressure and the composition of the original rock. Contact
Metamorphism Regional
Metamorphism
Further
increases in temperature and pressure will lead to higher-grade metamorphic
rocks as recrystallisation becomes more substantial and grains become
visible to the naked eye. In order, this may produce phyllite, schist,
and ultimately the very high-grade gneiss, which is characterised by a
black and white banded texture. If rocks undergoing metamorphism become too hot, they may actually melt and would then be classified as igneous when they solidify.
|
|