bE du rya
lapis lazuli [IW]
azure stone, lapis lazuli [RY]
Vaidurya or blue obsidian. A transparent blue gemstone that is, according to Thrangu Rinpoche and Chinese sources, the color of the sky and transparent, like a diamond or crystal. It is said to be extremely pure inside and out. It is not opaque. In Chinese it is called "leu li" which may well be a form of obsidian: there is a very rare clear dark blue variety of obsidian. It may also be blue beryl. It is not, however, lapis lazuli, which is opaque. Since there is doubt as to what it actually is, it may make sense to use the Sanskrit word Vaidurya in translations, rather than blue obsidian.
IW and RY, as well as just about every other English source, incorrectly translate this as lapis lazuli or azure stone. DKC