Welcome to the forum.
Speculation would seem to be pointless. All we know is it's black, partly shiny, and has some angular crystals of indeterminate size.
No indication of possible origin ('handed down' means nothing); opacity/translucency (try shining a light through it); hardness (try scratch testing it with a pocket-knife, window glass, penny or whatever and vice versa); streak colour (try scratching it on the back of an unglazed ceramic tile and blow away the dust); magntic properties (is it attracted to a magnet, and how strongly); density (is it unusually heavy or light relative to a stone of similar proportions); size (measure it, or include something for scale); or the crystal form (better pictures needed).