* Gneiss is a metamorphic rock: This means it's formed from existing rock (like granite) that's been changed by heat and pressure.

* Granite is a common source rock: Granite is a common igneous rock with light-colored minerals (like quartz and feldspar) and dark minerals (like mica).

* Wavy bands of dark and light layers: The heat and pressure of metamorphism cause the minerals in granite to align, creating distinct bands of light and dark minerals. These bands often have a wavy appearance, reflecting the intense pressure involved.

So, your description accurately captures the key features of gneiss.