Dikes are formed when this material fills a crack and hardens.
When this material surrounds an elevated area of land, kipukas are formed. Coulées are domes of this material. Argon can escape from this material, making potassium-argon dating possible. Dikes are formed when this material fills a crack and hardens. It is classified based on viscosity and darkness, both related to silica content, as felsic or mafic, which form rhyolite and (*) basalt. Temperature determines whether this substance takes a ropey form called pahoehoe ["pa-ho-ay-ho-ay"] or a stony and sharp form called aa ["ah-ah"]. It is created when magma travels through a conduit and rises above the surface of the earth. For 10 points, name this molten rock expelled during a volcanic eruption.
When this material surrounds an elevated area of land, kipukas are formed.
lava [accept magma until "pahoehoe"]