Igneous rocks with very fine grained mineral crystals (or even glass) form quickly at the Earth's surface and are known as Extrusive or Volcanic rocks.
(Igneous rocks with very fine grained mineral crystals (or even glass) form quickly at the Earth's surface; are known; as Extrusive or Volcanic rocks)
Igneous rocks with very fine grained mineral crystals (or even glass) form quickly at the Earth's surface
are known
as Extrusive or Volcanic rocks