Hooiberg is a 165 m (541 ft) high volcanic formation on the island of Aruba. It is located almost in the center of the island.
For the most part it consists of black, granite-like rock with white chalk veins called hooibergiet. This rare hooibergiet is deep below the earth’s surface caused by upwelling of magma (high pressure and high temperature). With the tectonic upliftment of the Caribbean plate, the rock came above sea level. All of the surrounding rock has been eroded because it was softer than the hooibergiet.