Francis John Turner was born in Auckland on 10 April 1904, the son of Gertrude Kingcome Reid and her husband, Joseph Hurst Turner, a Latin master at Auckland Grammar School. His father died in 1913, leaving Frank's mother to bring up four sons. Frank attended Auckland Grammar School from 1917 with scholarship support. In 1921 he entered Auckland University College where he gained awards that included a Senior Scholarship in geology and the von Haast Prize. He completed an MSc in 1925.
After working briefly for the New Zealand Geological Survey, Turner took up a position in 1926 as lecturer and assistant in geology at the University of Otago under Professor W. N. Benson. The two men had little in common apart from intense professional respect for each other, but they achieved a fruitful working association. Turner's first scientific papers, however, were co-authored in 1928 with his mentor at Auckland, Professor J. A. Bartrum. Turner later paid warm tribute to Bartrum, particularly for his adherence to the sound scientific principle of entertaining alternative views, all open to criticism and the test of future observation. This practice was scrupulously observed by Turner in his own teaching and writing.
In 1929 and 1930 he made pioneering geological expeditions to South Westland and described the serpentinites and peridotites of the lower Cascade River area. More importantly, aided by Benson's earlier experience in Scotland, he recognised in the Haast River transect what has become a classic example of progressive regional metamorphism involving transformation of vast, relatively unmodified accumulations of sediments into highly deformed and thoroughly recrystallised rocks. Subsequently, he carried out much-cited reconnaissance studies of the crystalline rocks at Lake Manapouri and Doubtful Sound.
Turner was married in Auckland on 29 August 1930 to Esmé Rena Bentham, a teacher at Otago Girls' High School. He was awarded a DSc in 1933 and became a fellow of the Royal Society of New Zealand in 1938. Following tenure of a Sterling Fellowship at Yale University in 1938–39, he became a pioneer in the emerging science of structural petrology, focusing his work on crystal-lattice orientation in relation to deformation processes in metamorphic rocks. In 1942 he was appointed senior lecturer in geology at Otago. He applied for the directorship of the New Zealand Geological Survey in 1945 and was disappointed at not gaining the position. He left New Zealand soon after to be associate professor of geology at the University of California, Berkeley. He was professor from 1948 until his retirement in 1971. He became an American citizen in 1953.
Turner had an encyclopaedic knowledge of igneous and metamorphic petrology, and the ability both in his teaching and writing to synthesise and summarise with rare clarity. His New Zealand researches culminated in a memoir published in 1948 on the mineralogical and structural evolution of metamorphic rocks, a volume widely regarded as the first truly modern treatise on metamorphism. After his move to Berkeley he became involved in a study of crystal-lattice orientation in rocks deformed experimentally at elevated temperatures and pressures. His chairmanship of the department of geology has been credited with developing it into one of the world's leading university departments of earth science. In addition to research papers, he produced a series of textbooks that have profoundly affected the teaching of petrology worldwide.
Turner travelled extensively. He was greatly concerned over the fate of liberal regimes in South America and personally did much to help scientists displaced by political developments there. In 1956 he was elected to the United States National Academy of Sciences. Among his many other honours were Guggenheim (1951, 1960) and Fulbright (1956) fellowships, and a visiting fellowship at Brasenose College, University of Oxford (1971–72). He received the premier award of the Mineralogical Society of America, the Roebling Medal, in 1985. His work was also recognised in New Zealand: he was awarded the Hector Memorial Medal and Prize in 1951 and an honorary DSc from the University of Auckland in 1965.
A bluff exterior and a distracting cast in one eye were intimidating to some students, but Turner was a warm-hearted friend and a generous colleague. He had a zest for life and a discriminating love of the arts and good wine. He and and his wife, Esmé, were well known for their hospitality. Frank Turner died in Berkeley on 21 December 1985, survived by his wife and a daughter. An obituary in The Times of London described him as one of the most distinguished petrologists of his generation.