Most people are surprised when they see bullion bar of gold, and the reason for the surprise isn't that it's gold what they are looking at, it's because of the dimensions which the bar has. Density of gold is still something with which a lot of people are not familiar and that is exactly the reason why most people are surprised.
Out of all the metals that we know of, gold has one of the highest densities. Density is important for a number of reasons but one of the more interesting ones is because it's what determined the weight of a certain element or a compound, to be more precise the weight of a certain size of an element or an compound. Difference between the same size block of Styrofoam and iron for example is familiar to everyone, at least it should be. Styrofoam will be a lot lighter because it has lower density than iron, same thing goes for gold and iron, where gold is almost three times as dense as iron. Roughly that would mean that the same size cube of gold would be 3 times more heavier than one made of iron.
When it comes to gold bars this is expressed even more, 1 troy ounce pure gold bar is so small that it can be held on the tip of your finger, at least the Credit Suisse i troy ounce gold bar can with diameter of roughly 1 X 1.5 inches. Same thing goes for the other popular weights of gold bar, 1 kilo, you would normally think that one kilo is large, but a gold bar of this size can fit in the palm of your hand, of course depending on what kind of dimensions it actually has. You could say that even though gold comes in small sizes it packs quite a punch, not just because of weight but also when you factor in the price that these bars have.