I believe they are volcanic in nature,like obsidian.whatever minerals that are in the area of heat and pressure can"*******ize"the parent rock causing limitless combinations.the smoother the slower it cooled on surface.Too much crystalline structure for a gemstone.I'm no geoligist,but I have seen examples,"in the wild"just like those.
pat.....p.s.most universities are happy to id for you.if they like,they may make an offer.