Quartz crystals have a number of powerful benefits that make them useful to use for meditation.
Quartz helps to amplify the energy of other crystals and to amplify your thoughts, so this may help you to more easily make a connection with your skull, or to Spirit using the skulls energy to advance this aim.
Although using quartz is not totally necessary, the unique properties of quartz, to amplify the energy is extremely valuable.
Quartz resonates well and will help you to more easily understand what is being communicated to you, when you are working with them.
Quartz may be especially helpful when you are doing a crystal skull meditation, when information may more than likely come through to you.