A simple example of a dissolved substance is the sugar that we place in our coffee. At first sugar is a solid substance that looks like small, hard, white grains of sand, but when it is mixed into water it becomes dissolved . We know the sugar is there because our coffee is sweet, but we can't see it because it is a dissolved substance . In Lesson 11, we learned that one of the dissolved substances in ocean water is salt. Another dissolved substance in ocean water is a type of rock called limestone .
Limestone is actually one form of mineral called calcium carbonate .
In a process called calcification, the zoaxanthellae-algae that live inside coral polyps can change dissolved limestone into solid limestone. When this happens the polyp takes the solid limestone, and lays it down under its body in a skeleton that has a certain pattern. The pattern in which the skeleton is laid depends on what species of coral polyp it is. Every different species of coral polyp lays down a different skeletal pattern . Many plants and animals use different forms of calcium carbonate in their bodies.