Robert "Bob" Louis "Luigi" Folk (September 30, 1925, Cleveland, Ohio – June 4, 2018)[1] was an American geologist and petrologist, specializing in sedimentology, sandstone petrology, and carbonate petrology.[2] He is known for the 1959 eponymous Folk classification of sedimentary rocks, which, with some minor modifications, is still in use today.[3][4] He is one of the founders of what is sometimes called "Soft Rock Geology".[1]