Densities of materials

material g/cm^3 lb/in^3 lb/ft^3   lb/gal 
water 1.00  0.036  62 8.35 
aluminum 2.70 0.098 169 22.53
zinc 7.13 0.258 445 59.50
iron 7.87 0.284 491 65.68
copper 8.96 0.324 559 74.78
silver 10.49 0.379 655 87.54
lead 11.36 0.410 709 94.80
mercury 13.55 0.490 846 113.08
gold 19.32 0.698 1206 161.23

The lb/gal column is used for comparison to a gallon of milk, which weights about 8.4 lb (it's mostly water).  If that milk were changed to aluminum, it would weigh about 22.5 lb.  If it were changed to gold, it would weigh about 161 lb (19 gallons of water)!  Did you notice that copper is heavier than iron?  A cubic foot of iron is 491 lb.  A cubic foot of copper is 559 lb.  Silver is even heavier than copper, at 655 lb for a cubic foot.  Gold is really heavy at 1206 lb for a cubic foot.  When you see a movie of thieves carrying bars of gold, you know they are faking it!