Molybdenite (mo-LIB-denite) is the only mineral that might be confused with graphite. It's dark, it's very soft (Mohs hardness 1 to 1.5) with a greasy feel, and it forms hexagonal crystals like graphite. It even leaves black marks on paper like graphite. But its color is lighter and more metallic, its mica-like cleavage flakes are flexible, and you may see a glimpse of blue or purple between its cleavage flakes.
Molybdenum is necessary for life in trace amounts, because some vital enzymes require an atom of molybdenum to fix nitrogen to build proteins. It's a star player in the new biogeochemical discipline called metallomics.