igneous rock crystals

Originally uploaded by griggans

When the molten rock cools slowly ( top slide / underground) the crystals are bigger.

When the molten rock cools quickly ( bottom slide / above ground) the crystals are smaller.

Remember, molten rock above ground is called lava, and below ground is called magma.

Igneous rocks formed above ground like pumice and basalt are called extrusive rocks. Ignous rocks formed underground like granite are called intrusive rocks. Because the crystals are larger, the intrusive rocks like granitse are much harder and denser. Pumice contains are bubbles and is not very dense.