More generally, a coarse granite occurring as vein material in other rocks.
Webster 1828 Edition
Pegmatite
PEG'MATITE
,
Noun.
Primitive granitic rock, composed essentially of lamellar feldspar and quartz; frequently with a mixture of mica. In it are found kaolin, tin tourmaline, beryl, aqua marina, tantale, scheelin and other valuable minerals.