There are three main types of coral reefs; coral reefs, coral reefs and atoll reefs. Coral reefs are the most common of the three as they grow directly from the shore, surrounding the islands as borders along the coast. When a coral reef continues to grow upwards from a volcanic island that has sunk completely below sea level, an atoll is formed. The atoll's coral reefs are circular/oval in shape and have an open lagoon in the center. Coral reefs are quite similar to fringing reefs as they also border the coast, but what differentiates them from a fringing reef is that they do not grow directly from shore, but are separated from land by an expanse of deep water. This creates a deep water lagoon between the shore and the coral reefs. Stony corals or stony corals are primary reef-building/hermatypic corals that have rigid skeletons made of calcium carbonate (CaCo3), which in crystalline form is known as aragonite. Hard coral colonies have many polyps cemented together by the calcium carbonate skeletons they create, and a layer of tissue covers the skeleton and connects the coral polyps for distr...