Asbestus (Gr. a substance unaffected by fire, from a privative and to quench), a term used rather to denote a peculiar form assumed by several minerals than to designate any particular species. Tremolite, actinolite, and other forms of hornblende, excepting those containing much alumina, pass into fibrous varieties, the fibres of which are sometimes very long, fine, flexible, and easily separable by the fingers, and look like flax. These kinds, like the corresponding mineral pyroxene, are called asbestus. Pliny supposed it to be a vegetable product, although good for making incombustible cloth, as he states. The amianthus of the Greeks and Latins was the same thing; the word meaning undefiled, and alluding to the facility of cleaning the cloth by throwing it into the fire. The colors vary from white to green and wood-brown. The name amianthus is now applied usually to the finer and more silky kinds. Mountain leather is a kind in thin flexible sheets, made of interlaced fibres, and mountain cork the same in thicker pieces; both are so light as to float on water, and they are often hydrous. The individual crystals of asbestus are easily separated from each other, are very flexible and elastic, and have a fine silky lustre.

A single fibre fuses into white enamel glass; but in the mass it is capable of resisting ordinary flame, and has hence been extensively applied in the manufacture of fire-proof roofing, flooring, steam packing, clothing, and lamp wicking. The ancients were familiar with its incombustibility, and wove a cloth out of it for the purpose of wrapping up the bodies of the dead when exposed on the funeral pile; they also made napkins of it, which were cleaned by throwing them into the fire; and they employed the finer varieties for the wicking of votive lamps. Gloves for handling hot iron and firemen's clothing have been made of it in Bohemia and France; and at one time it was thought that an important industry would grow out of this application, but experience has developed some practical difficulties, and asbestus fabrics are now a curiosity. The use of this material for a non-conducting envelope of steam pipes, for fire-proof roofing, and for safes, bids fair to become extensive. - Asbestus occurs abundantly in Switzerland, Italy, Scotland, on the island of Corsica, on Staten Island, and in numerous other localities.

A magnesian-iron hornblende called anthophyllite frequently occurs as a bowlder on the island of New York, and has been found in situ at the corner of 59th street and 10th avenue.