Hyalite in Hyalite Canyon
Near Bozeman Montana, Hyalite, a form of opal with a clear glassy appearance covers broken talus and rocks and sparkles like a gem in the afternoon light. I observed sections one-meter square that looked like bubbles of melted glass, poured over broken rock.
Greek for "glass stone", Hyalite is generally considered the purest and clearest Opal variety; A cut gem can have the appearance of clear cut glass. Hyalite is also called Muller's glass, jalite, and water opal.