Coral reefs & sources
A coral branch is the skeletal remains of a colony of coral polyps (such as on the above picture). Coral – as used in the context of precious coral- can either refer to the marine animal or the material produced from its skeletal remains. A polyp colony is composed of three different parts: the coenosarc, the sclerax and the polyps. The coenosarc is what binds the polyps to the skeleton. The sclerax is the hard skeleton left behind by the polyps and that can be used as a gem material. Corals have small growth rate ranging from few millimeters to 2cm per year.
Only a very few number of coral species have suitable properties that allow for them to be worked, and thereby be used in jewellery and for ornamental purposes. The reefs in which these different coral species vary greatly, as some Corallium rubrum reefs can be very shallow (10-200m) whereas Corallium secundum reefs around Midway were discovered at huge depths of 900-1500m.