The density of one rock unit relative to another. Density contrasts can be either positive or negative. For example, if Rock A = 2.30 g/cm³ and Rock B = 2.40 g/cm³ then the density contrast of Rock A relative to Rock B is -0.10 g/cm³. Conversely, the relative density contrast of Rock B relative to Rock A is +0.10 g/cm³.

Gravity anomalies caused by density contrasts within the earth's sedimentary section, crust and sub-crust can be analyzed and interpreted as lithologic and/or structural anomalies.