Hyalophane or jaloallofane is a crystalline mineral, part of the feldspar group of tectosilicates. It is considered a barium-rich potassium feldspar. Its chemical formula is (K,Ba)[Al(Si,Al)Si2O8], and it has a hardness of 6 to 6+1⁄2. The name hyalophane comes from the Greek hyalos, meaning "glass", and phanos meaning "to appear". Hyalophane has sometimes been used as a gemstone.