Skip to main content
Geosciences LibreTexts

16.29: Coral

  • Page ID
  • Coral
    Chemical composition Aragonite (CaCO3)or conchioline
    Crystal system Amorphous
    Habit Branching, tree-like
    Hardness 2.5 - 3.5
    Refractive index 1.48 - 1.56
    Specific gravity 1.37 - 2.60
    Lustre Waxy

    File:Coral beads.jpg

    Figure \(\PageIndex{1}\): Mediterranean Red Coral Beads

    File:Red coral.jpg

    Figure \(\PageIndex{2}\): Coral, Species: Scleronephthya

    Coral is one of the few organic gems. It is the exoskeleton of colonial polyps. These are small animals that create their branching homes from calcium carbonate dissolved in seawater. The colors of gem coral range from pale pink (angel-skin) to oranges and reds. Coral has been used throughout our history; it was pictured on a Sumerian vase dated at 3000 BC It was traded between the Mediterranean and India at the time of the birth of Christ. Coral was introduced into Mesoamerica by the Spaniards. Native Americans used it extensively in jewelry. Coral was used in Roman times to protect children from danger. It is still worn in Italy today to protect from the evil eye.

    G&G Articles on Coral 1934-1980

    The GIA has published all the G&G's from 1934 until 1980 online. The organization of the list by subject was done by Joseph Gill.

    • Spring 1950, Coral, the Forgotten Gem, by Copeland, p. 282, 6pp.
    • Fall 1959, Black Coral of Hawaii, p. 337, 1p.
    • Fall 1960, Black Coral of Hawaii, p. 72, 3pp.
    • Summer 1962, A White Coral Substitute, p. 304, 2pp.
    • Spring 1967, Black coral characteristics, p. 146, 1p.
    • Fall 1967, Dyed Angel-Skin Coral, p. 209, 1p.
    • Summer 1973, A partly silicified coral, p. 182, 2pp.
    • Fall 1973, Hawaiian Black Coral, by Webster, p. 196, 3pp.
    • Fall 1973, Silicified Coral, p. 206, 2pp.
    • Fall 1973, Lapidary of Black Hawaiian Coral, p. 232, 1p.
    • Winter 1974, Blue Coral, p. 369, 2pp.
    • Winter 1974, Hawaiian black coral, but with a golden sheen, p. 369, 3pp.
    • Summer 1979, An Examination of the New Gilson "Coral," by K. Nassau, p. 179, 7pp.
    • Winter 1979, Gold Corals – Some Thoughts on Their Discrimination, by Grahame Brown, p. 240, 5pp.


    • Gemmology 3rd edition (2005) - Peter Read
    • Was this article helpful?