Substance with a structure consisting of a systematically repeated pattern of atoms. This term is also applied to rock types made up of crystals, such as Rocks that have recrystallized in a solid state due to changes in temperature, pressure, and chemical environment. Click on Term to Read More rocks that recrystallized at high temperatures or pressures, or igneous rocks that formed from cooling of Molten silicate (rock) beneath the surface of a planetary body or moon. When it reaches the surface, magma is called lava. Click on Term to Read More.