US EPA

3657270 

Technical Report 

Relationship Of Mineral Habit To Size Characteristics For Tremolite Cleavage Fragments And Fibers 

Campbell, WJ; Steel, EB; Virta, RL; Eisner, MH 

1979 

NIOSH/00144518 

S 

English 

Size characteristics of tremolite (14567738) and the relationship to mineral habit are assessed. The classic crystal habit of asbestos (1332214) includes all of the following properties: aspect ratios ranging upward to 1000 to 1 or higher; very thin fibrils, generally less than 0.5 micrometer (microm) in width; very high and tensile strength; and parallel fiber growth in veins. Photomicrographic cross sections are shown for prismatic tremolite, acicular amphibole, fibrous tremolite, and tremolite asbestos. Optical data for tremolite in various habits is listed. Factors involved in crushing and grinding of amphiboles and the way in which the grains break or cleave are considered; breakage of asbestos fibrils and fiber bundles is significantly different from that of nonasbestos forms. Examination of samples using petrographic and scanning electron microscopy is described. Tremolite and actinolite (12172677) particles were counted and size characteristics correlated with the habit of the mineral. Aspect ratio of particles from milled tremolites are tabulated for various habits. A relationship is found between the number of particles of critical dimensions of greater than 10microm in length and less than 0.5microm in width, and the habit of the tremolite and actinolite prior to grinding. Only asbestos particles produce long, thin particles of the dimensions necessary to produce adverse biological effects.