Consider the crystal structure for pyrite (FeS2), also…

      Consider the crystal structure for pyrite (FeS2), also known as Fool’s gold, shown here.  Iron atoms are the larger brown spheres, while sulfur atoms are the smaller yellow spheres, as labelled.  This image depicts the cubic unit cell and all atoms shown here are at least PARTIALLY within this unit cell.  Based on this depiction, if you wanted to calculate the theoretical density of the material, how many of each atom would you count as being “fully inside” the unit cell?   Hint: The iron atoms sit on face-centered lattice sites.