pegmatite

 
Pronunciation: /ˈpɛgmətʌɪt/

noun

Geology
  • a coarsely crystalline granite or other igneous rock with crystals several centimetres in length: tourmaline occurs mainly in granites, pegmatites, and greisens [mass noun:, as modifier]: pegmatite dykes

Origin:

mid 19th century: from Greek pēgma, pēgmat- 'thing joined together' + -ite1