Cordierite is a blue magnesium aluminosilicate mineral that is sometimes utilized as a gemstone. Indeed, samples that have been procured from Sri Lanka are sometimes referred to as water sapphires. A synthetic variety of the mineral, however, which has a very low coefficient of thermal expansion and excellent resistance to thermal shock, is primarily used in items such as electrical insulators and high performance resistors. Among the other notable characteristics of cordierite is its pronounced pleochroism, or propensity to exhibit different colors when viewed along different axes. In fact, this aspect of cordierite is the origin of its alternate name, dichroite.