Definition of miarole

Also known as miarolitic pods, these are scattered coarse grained pods or layers, ordinarily several centimetres in maximum thickness, within medium to coarse grained igneous rocks, especilly granites. Their essential minerals are coarser-grained than their enclosing rocks, may be subhedral to euhedral, and generally pegmatitic in texture. Many of these pods contain crystal-lined cavities that are known as druses or miarolitic cavities. The internal zonal sequence is typically: alkali feldspar graphically intergrown with quartz, microcline, and a central filling of quartz. Miarolitic structures probably represent local concentration of gases during very late consolidation of the host rocks.