A discussion was provided of the unique mineralogical properties and dimensions of asbestos (1332214) paying particular attention to tremolite (14567738) asbestos, actinolite (77536664) asbestos and other varieties of these minerals. Descriptions were provided of the mineralogical properties of the asbestiform minerals including fibrillar structure, tensile strength, crystal forms, and the size and shape of asbestos fibers including bulk samples. The author states that in describing mineral samples for biological experiments, hand specimen descriptions, locations, chemical composition, microscopic properties and comprehensive dimensional data should be provided. If these data are available, the differences between cleavage fragments and asbestos fibers are obvious. Even fibrous nonasbestiform byssolite can be distinguished. It is essential that comprehensive data be published for all minerals used in biological experimentation in man in order to understand what properties of minerals make them carcinogenic.