“Metamorphosis” means a change in form. Metamorphic rocks form when existing “parent” rocks change because of intense heat and/or pressure. The deeper a rock is in the Earth, the more pressure it is under. There is also pressure from the boundaries of tectonic plates pushing together. Heat can come from being exposed to the hot material below the Earth’s crust. Remember that metamorphic rocks don’t melt from heat--igneous rocks form from liquid rock. The heat and pressure that form metamorphic rock changes an existing rock’s structure. It’s like a ball of raw pizza dough being flattened and baked in the oven. It doesn’t melt, just changes form! Slate is a metamorphic rock formed from the sedimentary rock, shale. Gneiss is another metamorphic rock formed from granite, an igneous rock. Marble forms when limestone morphs from heat and pressure.

Which of the following describes how metamorphic rock forms?

A
Tectonic plate boundaries break apart an existing parent rock.

B
An igneous rock deep in the Earth is exposed to hot material.

C
Molten rock solidifies and hardens on top of the Earth’s crust.

D
A parent rock is baked and melted into liquid rock in the Earth.