Metamorphic rock is formed underground through a process that changes a rock's molecular structure due to pressure, heat and chemical reactions. A metamorphic rock forms from a parent rock called a protolith. Depending on conditions, a protolith can transform into any metamorphic rock. Because protoliths are capable of undergoing vast changes, identifying them is sometimes difficult for geologists.Know More
Under extreme pressures, such as between two colliding tectonic plates, the minerals of a metamorphic rock group together and align to form foliation, which appears as stripes in the rock. One example of a heavily foliated rock is gneiss.
Alternatively, highly heated areas, such as near magma chambers, produce vastly different metamorphic rocks. One example is hornfels.
Another area for metamorphism is at a subduction zone where oceanic plates collide with and bend under continental plates. Because these high-pressure areas are near the ocean, they are cooler and produce different metamorphic results. One example of this is the creation of a blue mineral called glaucophane. This mineral in the rock foliates from high pressure and creates blueschist, a blue-tinted version of schist.
A protolith may change a number of times before reaching its final metamorphic stage. For example, gneiss may begin as shale that turns into slate, phyllite, schist and finally gneiss.Learn more about Geology
The rock cycle explains the changes rocks undergo from the time they are expelled from the earth's mantle in the form of magma to the time that they return to the mantle and become magma once more. This process takes place over millions to billions of years, depending on the conditions the rocks are subject to. Weather, heat, water and pressure are all forces that affect the rock cycle.Full Answer >
The specific type of rock that forms when magma cools at the Earth's surface is extrusive igneous rock. Igneous rock forms when magma cools, but where the magma cools determines the type of igneous rock that forms. Igneous rock gets its name from the Greek word for fire and is so called due to the extremely hot liquid from which the rocks originate.Full Answer >
The soft, metamorphic rock composed of talc is called soapstone, or steatite. Soapstone gets its name from its greasy or soapy feel. It can be blue, gray, green or brown.Full Answer >
There is no definitive evidence to fully explain the formation of mica as the process is still under scientific study as of 2015. However, mica formation is said to be closely associated with the lack of orthoclase feldspar in pegmatites, which is where the mineral is predominantly found.Full Answer >