Mineral collectors made a significant contribution to the development of mineralogy as a science and the rich variety of specimens found in the South West of England enabled Cornish collectors to play a significant part in this process. This volume contains 168 letters selected from the correspondence of three eighteenth-century Cornishmen - Philip Rashleigh, the Reverend William Gregor, and John Hawkins - with other British and European researchers. It illustrates the motives of collectors and the ways in which improvements in identifying and studying minerals were made. The letters between Rashleigh and his nephew Pole Carew show the initial stage of acquiring and exchanging specimens. Other letters by all three men reveal their contribution to cataloguing and classifying minerals. The Introduction to the volume discusses the archives and letters, and sets out the broader historical and intellectual context in which the three collectors were active. A chronological list of all relevant letters in the three men's archives also provides a unique reference source.