Rocks that have undergone internal structural or mineral changes as a result of external factors such as temperature, pressure or chemical environments are called metamorphic rocks. Some gemstones may be formed during the metamorphic processes; rubies, sapphires, spinels and cordierites can be found in marble with a high aluminum content; chrysoberyls, garnets and andalusites are found in schists with a high metamorphic degree; diopsides, epidotes and garnets can be found in contact metamorphic aureoles (regions of high temperature and low pressure); jade (jadeites) is formed in high pressure metamorphic environments.