Obsidian is a naturally occurring mineraloid that forms from volcanic lava as it is quickly cooled by water or some other such drastic temperature reduction. Sometimes called volcanic glass or black glass, it presents in a limited variety of colors. There is also an extremely rare form of deep red obsidian which has black streaks embedded in the matrix. Apache Tears is obsidian that has been rounded and smoothed by wind and water. There is no such naturally occurring stone as blue obsidian.
Blue obsidian is man-made using a similar process to that of leaded or stained glass.
Its metaphysical properties are the same as plane old ordinary window glass. This information relates to the crystal skull community at large because skulls are now being fashioned from this material. I might add that blue is not the only color sold as obsidian. There is also green, purple and aquamarine glass skulls exploding onto the market. Recent innovations have put inclusions into the matrix.