Final answer:
Graphite is the mineral that is also an element, composed entirely of carbon atoms.
Step-by-step explanation:
The mineral that is also considered an element among the options provided is graphite. Graphite is composed purely of the element carbon, in the form of a crystalline allotrope. Unlike minerals such as calcite, which is a compound consisting of calcium, carbon, and oxygen (CaCO3), or hematite, which contains iron and oxygen (Fe2O3), graphite's composition does not involve multiple elements but consists solely of one type of atom - carbon. This makes graphite not only a mineral but also an element on the periodic table.