Diolite (1927 – 1951) was a British Thoroughbred racehorse and sire. He was arguably the best British two-year-old of 1929, when he won three of his five races including the Coventry Stakes and the Molecomb Stakes. In the following year he won the 2000 Guineas and finished third when favourite for the Epsom Derby. He remained in training for another two years but won only one more race. After his retirement from racing he became a very successful breeding stallion in Japan.