Of an igneous rock or its structure: characterized by irregular cavities into which crystals project.
Late 19th century; earliest use found in Quarterly Journal of the Geological Society of London. From German miarolit- (in miarolitisch (H. Rosenbusch Mikrosk. Physiogr (ed. 2, 1887) II. 39; from Miarolit a type of granite + -isch)) + -ic. German Miarolit is from Italian (northern) miarolo a type of granite from the Lake Maggiore area in northern Italy (from Italian regional (Lombardy) miaroeu granite) + German -lit.