India was the most important source of diamond until 1728, when discoveries were made in Brazil. Among the important large diamonds found in India were the Koh-i-noor, the Great Mogul, and, very likely, the Hope Diamond. Like India, Brazil in turn declined as a major source of diamond with the discovery and efficient recovery of large quantities in South Africa. [Illustration: The Hope Diamond, because of its long and dramatic history and its rare deep-blue color, is probably the best known diamond in the world. By speculation, the Hope is linked to the famous “French Blue,” which was brought to France from India in 1668 to become part of the crown jewels of Louis XIV. The French Blue was stolen in 1792 and never recovered, but in 1830 an extraordinary 44.5-carat blue diamond—presumably cut from the missing gem—came on the market. It was purchased by Henry Thomas Hope of England and became known by its present name. In 1949 the gem was acquired from the estate of Mrs. Evalyn Walsh McLean by Harry Winston Inc., of New York. Ten years later, Harry Winston, Inc., presented the gem (shown here in actual size) to the Smithsonian Institution.] Diamonds are extremely rare even in diamond mines. For example, the famous South African mines contain only one part of diamond in more than 14 million parts of worthless rock. In spite of this, more than three tons of gem- and industrial-quality diamond were mined in 1963. Among the British crown jewels is a cut diamond weighing 530.20 carats (more than 3¾ ounces), one of several stones that were cut from the largest gem diamond ever discovered. The rough stone, known as the Cullinan Diamond, weighed 3106 carats (almost 1¾ pounds) when it was found at the Premier Mine in South Africa in 1905. [Illustration: The Portuguese Diamond, weighing 127 carats, is the 13th largest cut diamond on record. More unusual, it is from Brazil, and is thought to have been part of the Portuguese crown jewels. In addition to its brilliant color flashes, it has a slight milky fluorescence that causes it to “glow” even in artificial light. (Actual size.)] Diamonds vary from colorless to black and from transparent to opaque. As they come from the mines, they are graded into two groups, gem and industrial. Those whose color, imperfection, or shape make them useless as gems—more than 8 out of every 10 carats mined—are used in industry. Diamonds of industrial quality also are produced synthetically, and these are used primarily in the manufacture of grinding wheels. The best gem diamonds are flawless and are colorless or slightly blue. Their value depends on their color, clarity, cut, and carat weight. Most costly are those called fancies, which have a distinct color such as blue, pink, green, or deep yellow. PEARL