Hyalophane

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 – 6½. The name hyalophane comes from the Greek hyalos, meaning "glass", and phanos meaning "to appear".