I can say with absolute certainty this is not a stone. As in a rock. There is a sub section of geological science 'petrology' that is about rocks. You really meant 'mineral'.... amIrite? Rocks are made of minerals and minerals are made of chemicals (plural) -- with a exceptions like diamond that has only one chemical constituent.
So is it a mineral? It manifests the fracture patterns of glass. The man made ( mostly ) form of SiO2 which occurs in nature in minerals and rocks as various permutations of quarts depending on contaminants which influence characteristics such as color, opacity structure ... whatever. There are many many many forms.
If it is a mineral it is a mineral with a glass like structure. Obsidian does that. Gem minerals, on the other hand, usually manifest crystalline structures like particular atomic lattice alignments, fracture planes , growth faces...facets ... all that sort of thing.
Will you be coming back to tell us about how you acquired this? What do you know about it?