In the case of bitcoin, a strong case can be made that, even with secondary markets, certain virtual currencies lack the legal elements of material value and property.
We also have the ability to check where a particular consignment of coltan comes from: we have a database of the residual elements typical of each known mine and can thus check material, as with a fingerprint.
Plato believed that the first four corresponded to the elements of which the Greeks thought the material world was composed: fire, air, water and earth.