Asbestos

ASBESTOS is a general term embracing the fibrous varieties of a number of minerals. Of these, the hydrous magnesium silicate, chrysotile (H4Mg3Si209), a variety of serpentine, is the most abundant and useful to industry. All other types of asbestos belong to the amphibole group of minerals and are classified as: crocidolite, NaFe(SiO3), FeSiO3; anthophyllite, (MgFe)SiO3; amosite, also a ferromagnesium silicate but with iron content higher than that of anthophyllite; tremolite, CaMg3(SiO3)4; and, actinolite, Ca (MgFe)3(SiO3)4. PROPERTIES The commercial value of asbestos depends largely on the physical property that permits it to be readily separated into fine filaments of high tensile strength and flexibility, which, coupled with the fact that it has the quality of incombustibility of a mineral-in distinction to vegetable and animal fibers-makes it of unique usefulness for many purposes. To some extent, the value depends upon the length of the fiber, although extreme length is neither necessary nor desirable for most purposes. Chrysotile occurs as cross-fiber veins, in which the asbestos fibers are approximately' at right angles to the vein walls, with vein width- or fiber length-seldom exceeding 2 or 3 in.; also as slip-fiber, in which the fibers 'lie in the same plane as the vein or on slippage planes. A cleanly broken vein of cross-fiber has a pearly luster and may range from a deep green or brown color to light shades of yellowish green or cream. When of good quality, the fiber filaments forming the vein may be easily drawn away from their neighbors and exhibit a fine silkiness and pure white color. They may be twisted into a thread and when flexed between thumb and fingers are found to be strong and pliable. Chrysotile withstands comparatively high temperatures without breaking down completely or fusing but begins to lose water of crystalliza-