Alfred Harker FRS (19 February 1859 – 28 July 1939) was an English geologist who specialised in petrology and interpretive petrography. He was Lecturer in Petrology at the University of Cambridge for many years, and carried out field mapping for the Geological Survey of Scotland and geological studies of western Scotland and the Isle of Skye. He and other British geologists pioneered the use of thin sections and the petrographic microscope in interpretive petrology. Education and career Harker's father was the Yorkshire corn merchant Portas Hewart Harker, his mother Ellen Mary Harker. He attended Hull and East Riding College, and the private Clewer House School (Windsor) before enrolling as an undergraduate at St. John's College (Cambridge) from where he graduated with an M.A. on 18 January 1882. Whilst at Cambridge he was an early member of the Sedgwick Club. In 1884 he held the post of Demonstrator in the Geology Department under Thomas McKenny Hughes (whom he regarded his mentor), as lecturer at Newnham College in 1892 at St. John's College, as University Lecturer in 1904, and as Reader in Petrology in 1918. Harker's duties included teaching Mineralogy and Petrology to students. Harker was elected as a Fellow of St. John's College in 1885. A geological tour of Western Europe in 1887 introduced him to the metamorphic rocks of the Ardennes which proved to be an influential experience to his continuing research. Harker accompanied Professor Thomas McKenny Hughes to the United States in 1891 where they attended the 5th International Geological Congress. This was the first time the event had been held outside Europe. Fieldwork and research In 1895, Harker commenced employment with the Geological Survey of Great Britain on a part-time basis. Professor McKenny-Hughes had also worked with the Survey, but Harker's invitation came from the then Director General, Archibald Geikie. This was to assist in the mapping and determination of the igneous rocks of the Isle of Skye and the Small Isles. This association lasted until 1905. At this time, he also became a Member of the Scottish Mountaineering Club. Harker's active fieldwork programme also saw him collaborating with Professor John Edward Marr of the Department of Geology on the volcanic rocks of the Lake District in 1889. The Sedgwick Museum of Earth Sciences opened in 1904 and three years later, Harker published research on material he had prepared petrological rock slices of. He named the petrological samples