Atlas Obscura has a post about the the largest diamond found in the last century.  It weighs 1,111 carats and measures 2.6 by 2.2 by 1.6 inches.  It was found in a mine owned by the Lucara Diamond Corporation.  Previously, the largest diamond discovered in this century was a measly 603 carats.  That diamond was cut into 26 separate diamonds and was set into a single necklace.  The largest diamond ever found is the Cullinan diamond, which was discovered in 1905.  That diamond was cut into 105 separate stones, with the largest two being part of the British Crown Jewels.