pegmatites

/P EH1 G M AH0 T AY0 T S/
noun
  1. 1

    A coarsely crystalline igneous or plutonic rock composed primarily of feldspar and quartz, normally with muscovite and/or biotite mica.

Source: https://en.wiktionary.org/wiki/pegmatite, https://en.wiktionary.org/wiki/pegmatites