Corals are major contributors to the physical structure of coral reefs that develop in tropical and subtropical waters. Due to its unique and striking color, red coral has become a popular gemstone choice for jewelers in recent years. Pure red coral, also known as 'fire coral' or 'ox blood coral' is becoming very rare due to the high demand for perfect specimens used in jewelry making, and the stress that over-collection is placing on the environmental health of coral reefs.
A single coral "head" can be the home to thousands of individual polyps, each polyp only a few millimeters in size. A colony of polyps function as a single organism, sharing nutrients via an interconnected gastrovascular system. All of the polyps in the colony are clones of each other, sharing the same genetic code. Each new polyp generation lives on the main calcareous skeletal (exoskeleton) that is the remains of previous generations.
The coral formation process creates a structure that is unique to the particular coral species, but the ultimate physical characteristics of each coral species is also subject to environmental influences. It is believed that corals first appeared during the Cambrian period, around 570 million years ago, yet Cambrian corals are extremely rare as fossils. Fossilized Rugose and Tabulate corals from the Ordovician period around 488 million years ago, are fare more prevalent.
Conchiolin & Calcareous Coral
There are two distinct types of coral: Calcareous Coral which is primarily composed of Calcite, and Conchiolin Coral which is primarily composed of protein. Formation of a calciferous exoskeleton involves deposition of calcium carbonate by the polyps from calcium ions that are isolated from the surrounding seawater. Conchiolin forming proteins are made up of organic macromolecules consisting of polysaccharides and proteins bound together with aragonite crystals.
Red coral is a semi-translucent to opaque material that is frequently dyed to enhance color. Corals can also be impregnated with resins or epoxies to fill surface fissures and flaws.
Black and Red Corals used in jewelry are Calcareous Corals that are much softer than other gems, with a hardness of only 3.5 to 4.0 on the Mohs scale. Fire Red Coral has a refractive index of 1.486 and a waxy to vitreous luster.
Chemical Composition of Calcareous Coral: CaCO3
Reconstituted Coral
Reconstituted coral is made from natural solid material, or coral fragments that have been pulverized into a powder, soaked in binding agents, then pressed into a solid mass to be re-cut. This can also be accompanied by dying to enhance color.
Semi-Precious Stones