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
Cave of the Crystals Cave of the Crystals Cave of the Crystals or Giant Crystal Cave () is a cave connected to the Naica Mine at a depth of , in Naica, Chihuahua, Mexico. The main chamber contains giant selenite crystals (gypsum, CaSO·2 HO), some of the largest natural crystals ever found. The cave's largest crystal found to date is in length, in diameter and 55 tons in weight. When it was accessible, the cave was extremely hot, with air temperatures reaching up to with 90 to 99 percent humidity. The cave is relatively unexplored due to these factors. Without proper protection, people could