Is coral a rock if so how is it formed and what type is it?

Answer 1

Coral is not really a rock. Corals are groups of living animals belonging to a group called cnidaria which also includes jellyfish and hydras and other simple animals. Cnidaria do not have any organs, but their entire bodies consist of two layers of tissue.

A coral animal is a soft-bodied cnidarian known as a polyp; genetically identical polyps (the offspring of one individual) gather together in colonies and together they build a skeleton around themselves out of calcium carbonate (the same mineral that makes up most of chalk, eggshells and limestone.) It is this calcium carbonate skeleton that we usually think of as "coral," as the soft animals are usually very small and hidden away within it.

Given enough time and the right conditions to multiply and grow corals can grow from small colonies to huge skeletons and colonies that can form real geographical features that shape the planet's surface; coral reefs, islands and atolls are a few examples. The Great Barrier Reef in Australia for example is clearly visible from space. Because the coral polyps in the Great Barrier Reef are genetically identical and share the same skeleton it has been argued that this reef should be classified as one organism - the largest organism on the planet!

The way in which coral polyps form their skeletons depends highly on factors like the composition and temperature of the ocean they live in. Corals are therefore very useful as indicators to tell us about how the climate is changing, as experts can tell what kind of conditions were like when the coral skeleton was formed. Coral polyps are very vulnerable to climate change - given their great beauty, importance to the global ecosystem (after all, they are the only animals other than humans that can form islands and reefs that change the planet's geography!), and use to humans in tourism, jewelery (made from the beautifully colored skeletons), construction (seriously, those skeletons are tough!) and climate research, corals are well worth preserving!