hyalite

/ˈhaɪəlaɪt/
noun
  1. A clear, glassy variety of opal that looks like colorless glass or ice.
    • Hyalite is sometimes called 'Müller's glass' because of its transparent appearance.
    • Collectors prize hyalite for its unusual, water-clear look.
    • The jeweler showed me a beautiful piece of hyalite that sparkled like frozen water.