These rocks are a type of rock formed from the solidification magma or lava. They can be formed above ground and underground. These types of rocks are classified igneous rocks and there are two types: intrusive and extrusive. Intrusive is formed when the magma cools and solidifies within the earth’s crust and extrusive cools and solidifies outside the earth’s crust and does so at a much faster rate. Igneous rocks are the oldest classification of rocks. The earth’s crust is composed of over 95% igneous rock with the rest being split between sedimentary and metamorphic rocks.
These rocks are transformations of existing rocks, meaning that these rocks must be classified as metamorphic rocks. They have been subject to some kind of high pressure or temperatures causing chemical or physical changes to the rocks. Metamorphic rocks are classifies my chemical and mineral assemblage know as metamorphic facies. These types of rocks are often formed when tectonic processes occur, such as continental collisions.
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