If you clear volume in the density equation:
[tex]\rho = \frac{m}{V}\ \to\ V = \frac{m}{\rho}[/tex]
The greater the density the lower the volume. This means, the volume of gold nugget will be smaller than the volume of iron pyrite nugget.
[tex]V_{gold} = \frac{m}{\rho} = \frac{50\ g}{19.3\ g/cm^3} = \bf 2.59\ cm^3[/tex]
[tex]V_{iron} = \frac{m}{\rho} = \frac{50\ g}{5.0\ g/cm^3} = \bf 10\ cm^3[/tex]
