Densities of Common Rock Types

The rock densities in the table below are expressed as specific gravity, which is the density of the rock relative to the density of water. That's not as strange as you may think, because water's density is 1 gram per cubic centimeter or 1 g/cm³. So these numbers translate directly to g/cm³, or tonnes per cubic meter (t/m³). As you can see, rocks of the same type can have any density in a range of densities, since they can contain different proportions of minerals and voids.

Rock densities are useful to engineers, of course. But they're also essential for geophysicists who must model the rocks of the Earth's crust for calculations of local gravity.

Rock density is very sensitive to the minerals that compose a particular rock type. Sedimentary rocks (and granite), which are rich in quartz and feldspar, tend to be less dense than volcanic rocks. And if you know your igneous petrology, you'll see that the more mafic a rock is, the greater its density.