Defintely not molybdenite and probably too hard for stibnite as well. Arsenopyrite or pyrite. Once you get your eye in the colour is the best clue (pyrite tends to be more brassy in colour, arsenopyrite more silver but they can be similar - I get it right nearly every time but I have seen a lot). Streak and hardness are very similar, both can have parallel striae on their surfaces, neither has good cleavage. Neither dissolves in common, cold acids. They have different crystal forms (you would need a hand lens) - pyrote forms cubes and octahedra but arsenopyrite does not, arsenopyrite twins are common in slate in the Victorian goldfields (in the form of a cross as a rule), pyrite does not and is often seen as disseminated cubes - arsenopyrite crystals never form equidimensional forms (cubes, octahedra) but pyrite forms do. Arsenopyrite crystal fprms tend to be more elongate in one of their dimensions (imagine taking a cube and flattening it by pressing on one of its pointed corners until it becomes elongate).
I will start a blog on mineral identification if there is interest - perhaps both principles of identification and drawing members identification problems together into one place.