Size distribution measurements of South African actinolite asbestos (ferro-actinolite) by scanning electron microscopy. This material was characterized by the University of Maryland in collaboration with the US Bureau of Mines as part of studies on the nature of asbestos. The sample was provided to the University of Maryland by the US Bureau of Mines. The actinolite sample is from the Northern Cape province, South Africa. Sample obtained and measured ca. 1980. Data values were obtained with Scanning Electron Microscopy (SEM) with Energy-Dispersive X-Ray Analysis (EDXA) capability. See documentation file for full study abstract, an explanation of the content of the data files, and references to associated publications. The csv version contains the same data as the corresponding xlsx file. The csv file is provided as a software-independent alternative to the xlsx format.