Precious Corals - Treasures From The Depths

By Antonia Čirjak on January 22 2020 in Environment

Coral underwater.

Precious Coral has entered the English language as a description of the rich, youthful color of beauty -  the unique shade of orange-red that belongs on the fairytale princess’s lips.

The color of many precious corals has been announced as the ‘Color of the Year 2019’ by Pantone, a company known for its proprietary color system widely used in the printing industry. Under the name ‘Pantone 16-1546 Living Coral’, this color code alludes to the pink to red color that is commonly associated with corals.

These days, the demand for precious corals is falling, mainly because of their endangered status but also because they cannot be cultured.

Where Does The Precious Coral Come From?

Precious coral belongs to the group of organic gems - gemstones of the biological origin. Corals are made by coral polyps, tiny marine colonial animals. Gem-quality coral, called Precious Coral, is related to reef-forming coral but represents only a small fraction of all the enormous variety of coral species and types. 

Couple of scuba divers on a coral reef.
A couple of scuba divers on a coral reef.

Precious coral is mainly a species of coral that prefer dark environments and rocky beds with little sedimentation, very different from our perception of the sunny shallow reef ones. Precious corals come from the depths of over 500 feet deep or dark caves and caverns. These biological formations grow very slowly, sometimes only 1 millimeter per year. The most valuable varieties come from the Mediterranean, especially Sardinia, the Red Sea, and some areas of the Pacific around Japan, Taiwan, and Australia. Precious coral of a golden undertone also grows in Hawaii, but it cannot be harvested and exported from the USA under the Lacey Act. 

Black and golden Antipatharia corals are found around the Philippines and Indonesia. They differ from other corals in so much that their skeletons are made up of organic matter (closely related to keratin), not of calcium carbonate. Although flexible when growing, the material becomes rigid after fishing. These corals are protected and hence rarely available. 

But Why Is It So Valuable?

Precious coral is valued for its intense coloration and a vitreous luster. The skeleton of the coral is made out of calcium carbonate colored by carotenoid pigments. Unpolished coral can look dull, but once a professional works with it, the reason for its fame becomes obvious. The coral is opaque and very rarely translucent. 

Underwater coral reef.
Underwater coral reef.

Coral can have a range of reddish-pink colors that go from orange-pink to deep-red. Blue and black corals are not often used for gems or jewelry, as their trade is heavily regulated.

Is It Legal To Harvest And Sell Precious Corals?

The source of the precious coral is mainly species from the genus Corallium, Pleurocorallium, and Hemicorallium. Because corals are living creatures and a fundamental part of vulnerable ecosystems, many of the varieties are protected by environmental and wildlife protection agreements. Regulated coral includes Corallium japonicum, Corallium elatius, Corallium secundum, and Antipathes grandis. Although these may require permits for international trade, they can usually be traded domestically.

Most coral gemstones available today are varieties of Corallium rubrum, a very specific pink to red-colored species of the coral genus. Corallium rubrum is not included in international protection acts making it easier to import and export to most countries.  In the trade, Corallium rubrum is one of the 'noble corals’ together with 'angel skin coral,' a pink to salmon-colored coral. 

What Are The Gemstone Properties Of A Precious Coral?

Considering that coral is actually organic material, it is not really durable but can be reasonably hard. The hardness, however, is not nearly as close to that of gemstones. They are also sensitive to acidity, and heath.

Eastern ornaments.
Eastern ornaments.

When carefully polished, it can be used for anything from pieces of jewelry to even plates. The branch-like shape, preserving coral’s natural form, is unique to this gemstone.

Is Natural Fossil Coral Different From Precious Coral?

Precious corals are modern specimens. Fossil corals are ancient corals that were buried in the sediment millions of years ago as the oceans rose and disappeared. Those ancient corals underwent the process known as agatization. The natural materials in the corals got replaced by agate (chalcedony) from the silica-rich ground waters seeping through the limestones.

In Indonesia, entire coral heads are often entirely preserved and appear just as they did 20 million years ago. However, their density is much changed by replacement with silica, iron, manganese, and other minerals. There are fern corals, brain corals, hex corals, honeycomb corals, and many more.

Agatized fossil coral is different from the agates of other origins because it preserves the internal structures and patterns of the coral. Fossil coral pieces are sought by gemstone and fossil collectors around the world. Additionally, fossil corals are much more durable than modern corals because agate is relatively hard (7 on the Mohs scale) so fossil coral has broader applications in jewelry.

Florida and Georgia in the USA are also important sources of fossil coral. In fact, Florida has declared fossil coral to be the Florida State Rock.

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