The Cullinan diamond, discovered in South Africa in 1905, was cut into nine gem-quality diamonds. (These are glass replicas!) The largest, nicknamed the "Star of Africa," is part of the British Crown Jewels.
Photograph by Chris 73, courtesy Wikimedia. CC-BY-SA-3.0

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    On January 26, 1905, miners in South Africa unearthed the Cullinan diamond, the largest gem-quality diamond ever discovered.
    Diamonds are minerals that form from an unusual type of magma, called kimberlite, deep in Earth’s mantle. Kimberlite forms in a deeper area of the mantle, is subjected to greater pressure, and contains more water and carbon dioxide than most magmas. Diamonds form as kimberlite violently erupts on Earth’s surface.
    The Cullinan diamond, a whopping 3,106 carats and weighing about 621 grams (1.4 pounds), was cut into nine stones. The largest, nicknamed Cullinan I or the “Great Star of Africa,” is 530 carats. Today, the Great Star of Africa sits at the top of a scepter, part of the Crown Jewels of the United Kingdom.
  • Term Part of Speech Definition Encyclopedic Entry
    carat Noun

    unit of weight, used for gems, about 200 milligrams.

    diamond Noun

    type of crystal that is pure carbon and the hardest known natural substance.

    erupt Verb

    to explode or suddenly eject material.

    gem Noun

    mineral, rock, or organic material that can be cut and polished for use in jewelry.

    kimberlite Noun

    type of magma or igneous rock associated with diamonds.

    magma Noun

    molten, or partially melted, rock beneath the Earth's surface.

    Encyclopedic Entry: magma
    mantle Noun

    middle layer of the Earth, made of mostly solid rock.

    Encyclopedic Entry: mantle
    miner Noun

    person who excavates metal or other materials from the Earth.

    mineral Noun

    inorganic material that has a characteristic chemical composition and specific crystal structure.

    rock Noun

    natural substance composed of solid mineral matter.

    scepter Noun

    symbolic staff or rod carried by a monarch or other ruler.