Today, the batholith constitutes the main part of the Aruban landscape. Big, round boulders of tonalite are the result of the way that tonalite weathers, called spheroidal weathering. Another rock in the batholith is gabbro, a black coarse, grained variety of tonalite named hooibergite. The batholith and the Aruba Lava Formation both contain dikes and veins. Dikes occur when igneous rock penetrates another rock and creates a sheet-like formation that cuts across the penetrated rock.
Veins are depsoits of foreign material within a rock fracture.
Gold, such as that found in the rroois on Aruba, formed in veins of a hard, white mineral called quartz. Sediments Limestones are the youngest rocks that make up Aruba and that surround the island's older rocks. Limestone formed after and on top of the older rocks. Limestone formed very differently than earlier rocks. Most limestone formed under water in an environment that is similar to the present-day marine environment where coral reefs grow.