The Palisades are made of igneous rock, specifically a type called diabase. Diabase is a dark-colored, fine-grained rock that is rich in plagioclase feldspar and pyroxene.

It was formed millions of years ago by volcanic activity, when magma from deep within the Earth's crust intruded into existing sedimentary rocks. The magma cooled and solidified, forming the diabase that we see today.