The membranolytic activity of ten quartz specimens, determined quantitatively as the percentage of erythrocytes lysed as a function of mineral concentration, varied by up to 100 times depending on particle size, method of size reduction, thermal treatment, dispersal in the experimental system, and quartz variety. Five specimens that are currently used as standard fibrogenic dusts in pneumoconiosis research laboratories were obtained as fine powders. Two other specimens obtained as large single crystals and three additional ones obtained as massive crystalline specimens required pulverization before testing. The specimens were studied as size-heterogeneous powders, and after fractionation into narrow size bands. The membranolytic activity of the size fractions increased by an average of 30 times as the Stokes' diameter of the particles decreased from 20 to 1 μm. The five specimens that were reduced to powders in a carborundum mortar and pestle lost activity after hydration in the water-fractionation process. When these inactive quartz specimens were heated to 400-500°C for 6 hr, their activities were restored. The active and inactive quartz specimens were indistinguishable by electron microscopy, powder X-ray diffraction and optical microscopy. The physico-chemical properties of quartz are variable and therefore the mineral's biological potential varies considerably.
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