Igneous rock the partial melting of rocks within the mantle and crust. Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks. They are formed by the cooling of molten magma on the earth's surface. The magma, which is brought to the surface through fissures or volcanic eruptions, solidifies at a faster rate. Hence such rocks are smooth, crystalline and fine-grained. Basalt is a common extrusive igneous rock and forms lava flows, lava sheets and lava plateaus. Some kinds of basalt solidify to form long polygonal columns. The Giant's Causeway in Antrim, Northern Ireland is an example. The molten rock, with
Lava Cast Forest 1942, the United States Forest Service designated 5,120 acres as part of the Lava Cast Forest Geological Area and were promoted as a tourist attraction. In 1963, scientists from NASA became interested in the lava fields because they had very little erosion and they suspected it might be what they would find on the surface of the Moon. From 1964 to 1966, at least 46 astronauts trained for lunar missions in the area. James B. Irwin delivered a rock from one of Oregon's lava flows to the lunar surface to commemorate NASA's experiences in central Oregon. Lava Cast Forest Lava