The picture below shows a boulder made of gneiss. Gneiss forms deep underground due to heat and pressure and has observable layers. Which type of rock is gneiss?

Gneiss is a type of metamorphic rock which forms itself from a pre-existing rock.

Explanation:

The shown rock boulder is Gneiss which is a type of metamorphic rock which forms from the application of heat and pressure to the pre- existing rock which exists in the deeper crust of the Earth.

The formation of Gneiss occurs at the igneous rock or sedimentary rock by heat and pressure as foretold. It can be distinguished easily by the bands of darker and lighter pattern as seen in the boulder picture. There exist no distinct foliation among the bands pattern of the rock formed.