Metamorphic Rocks

Metamorphic rocks are unique in that they form exclusively beneath Earth’s surface. They develop when existing rocks are subjected to intense heat and pressure, which causes both physical and chemical changes in their mineral composition. These conditions are commonly found at convergent plate boundaries, where tectonic forces generate significant pressure, or in areas where molten magma comes into contact with surrounding rock, raising temperatures enough to trigger metamorphism.

Types of Metamorphic Rocks

Metamorphic rocks are divided into two main types: foliated and non-foliated. Foliated metamorphic rocks have a clear layered or banded appearance. This forms when the original rock (called the parent rock) contains flat, plate-like minerals. Under intense heat and pressure deep within the Earth, these minerals are squeezed and rearranged so that they line up in parallel layers. This alignment gives foliated rocks their distinct striped or layered look. A common example is slate, where strong pressure flattens the minerals into thin, visible layers.

Non-foliated metamorphic rocks, on the other hand, do not have a layered appearance. Their minerals do not line up in sheets because they are usually made of minerals that are not flat or are arranged randomly. Instead of forming layers, these rocks tend to look more solid and uniform throughout. Non-foliated rocks often form when heat is the main factor in changing the rock, rather than pressure that pushes minerals into alignment. Examples include marble and quartzite, which have a smooth, even texture without visible layers.