What rock can only form from contact metamorphism? Hornfels Anthracite Coal

Hornfels is a rock that can only form from contact metamorphism. Here's a step-by-step explanation:

1. Contact metamorphism occurs when rocks are heated by contact with magma or lava. This process changes the mineral composition and structure of the rock without melting it.

2. Hornfels is a fine-grained nonfoliated metamorphic rock produced by contact metamorphism.

3. The intense heat from the magma or lava causes the minerals in the original rock to re-crystallize and form new minerals. This process is called recrystallization.

4. The new minerals form in a random, interlocking pattern, which gives hornfels its characteristic dense and hard texture.

5. Therefore, hornfels can only form from contact metamorphism.

On the other hand, Anthracite Coal is a type of coal that has undergone metamorphism. It is the highest rank of coal due to its high carbon content and is formed from bituminous coal when great pressures are exerted over it. This process is not exclusive to contact metamorphism.