Cordierite is an aluminum and magnesium silicate mineral with two main uses: as a gemstone (iolite) and as an industrial ceramic material. As a gemstone, it is prized for its colors, which range from blue to violet, and its strong trichroism, and was used by the Vikings for navigation on cloudy days. As a ceramic, it is notable for its high resistance to heat and thermal shock, making it ideal for pieces that withstand extreme temperatures.