pegmatite
noun
peg·ma·tite ˈpeg-mə-ˌtīt 
: a coarse variety of granite occurring in dikes or veins
pegmatitic
ˌpeg-mə-ˈti-tik
adjective 
Word History
Etymology
French, from Greek pēgmat-, pēgma something fastened together, from pēgnynai to fasten together — more at pact
First Known Use
circa 1828, in the meaning defined above