Hyalite is a form of opal with a glassy and clear appearance which may exhibit an internal play of colors if natural inclusions are present. It is also called Muller`s glass, water opal and jalite. The name Müller`s glass derived from the name of its discoverer, Franz-Joseph Müller von Reichenstein. Hyalite`s Mohs hardness is 5.5 to 6 and has...... Found on http://en.wikipedia.org/wiki/Hyalite
Hy'a·lite noun [ Greek 'y`alos glass: confer French hyalite .] (Min.) A pellucid variety of opal in globules looking like colorless gum or resin; -- called also Müller's glass . Found on http://www.encyclo.co.uk/webster/H/74