Rocks = clusters or aggreates of various minerals. There are three types of rocks -igneous, sedimentary, and metamorphic. Igneous rocks = fire rocks- formed by the cooling of magma. Magmas with different chemical makeups and different cooling rates, form different igneous rocks. Lava = magma which has reached the earth"s surface. Volatiles = typically h2o & co2 - quickly convert from liquid to gas = volume they make an eruption explosive. They make lava flow quicker by lowering a rocks melting point. volatiles are liquid because of pressure from overlying rock. As magma rises pressure - liquid flashes to gas - like a shaken up pop can. More silica = thicker magma = stronger influence than volatiles m. p. Factors influencing magma include temp. , pressure, volatiles, & silica content. Basaltic magma = 900-1200/1400 c, about 50% silica, and a small %age of volatiles. Often cools under the ocean = cools quickly = smaller crystals.