Coral

According to Greek legends, coral is the blood spilled by the hero Perseus when he cut off the head of the monster Medusa. In fact, coral is skeletal material produced by marine animals. Coral is organic and created by living organisms. When coral polyps die, the hardened skeleton remains and this material is used as a gemstone. Most corals are white, but nature can create coral in many other colors, including the popular orange to red forms. Usually its compound is calcium carbonate. Corals have a dull appearance when collected and are then polished. Precious corals, which are red and pink in color, are found around Japan and Malaysia in African coastal waters and the Mediterranean. Black corals are mined from around the West Indies, Australia and Pacific Islands.

Coral is a gemstone that has been used for thousands of years. Besides the beautiful solid colors found in Coral, there may also be color zones or swirls where white, pink, orange and red are most common.

Coral gemstones can be solid or porous depending on polyp formation. Despite Coral’s beautiful colors, it is very soft and brittle and does not make a durable gemstone. It is prone to both scratching and chipping.

Varieties:

• Black Coral: Black colored marine coral species from the Antipatharia family.

• Precious Coral: Also known as Red Coral. Precious Coral has a natural pink to red color and is Coral’s most desirable form of jewellery.

• Red Coral: The marine coral species corallium rubrum (or several related species) with a natural color from light pink to deep red.

Mineral Group: Organic Minerals

Mineralogy: Mostly calcium carbonate (CaCO3)

Environment: Corals are primitive animals belonging to the Phylum Coelenterata or Cnidaria and are found anywhere in the world’s ocean at depths ranging from the tidal mark to the abyss, up to 6000 m.

Physical Properties

Crystal habitAmorphous
ColorWhite, Red, Orange, Pink, Gray, Black
LusterVitreous, waxy
CleavageNone
DiaphaneityTranslucent to opaque
Mohs Hardness3 – 4
Density2.6 – 2.7

References

  • Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  • Gem notes: Gemstone Information. Fire Mountain Gems and Beads. (n.d.). Retrieved October 24, 2021, from https://www.firemountaingems.com/resources/encyclobeadia/gem-notes/gmstnprprtscrl1.
  • Minerals.net. 2021. Coral: The gemstone coral information and pictures. [online] Available at: <https://www.minerals.net/gemstone/coral_gemstone.aspx> [Accessed 24 October 2021].
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