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The report includes (1) detailed descriptions of the process of mining and quarrying pegmatite rock, the milling of its major constituents, mica, feldspar and quartz, with a section on hydraulic mining and processing of kaolin; (2) the concentration of atmospheric dusts generated in these different processes; (3) complete medical data obtained from examining fifty-seven men exposed to fine silica-free mica dust, thirty-one men and seventy-eight women fabricators of sheet mica, ninety-five men exposed to kaolin dust, 741 men mining the pegmatite and sorting its chief constituents, and a control group of 245 applicants for work who had had no previous exposure to dust.
For details of this carefully conducted study one must consult the original paper. The chief conclusions of the report were that the inhalation of fine mica dust generated in grinding this material caused a pneumoconiosis demonstrable clinically and by x-ray examination, that the fabrication of sheet mica
Pneumoconiosis Among Mica and Pegmatite Workers. JAMA. 1940;115(18):1571–1572. doi:10.1001/jama.1940.02810440063025