DOM 017a Sulfide Pyrite FeS2
The most common sulfide you will find (although even finding this requires some effort). Unlike the next most common sulfide - chalcopyrite, it splinters with no cleavage plane. Chalcopyrite is more malleable without the numerous sharp edges. The main issue will be differentiating this from metal oxides. Magnetite is similar but magnetic...
Detrital Optical Mineralogy reference material.