ASTERIA is also the name of a gem, usually called the cat's eye, or oculus cati. It is a very singular and very beautiful stone, and somewhat approaches to the nature of the opal, in having a bright included colour, which seems to be lodged deep in the body of the stone, and shifts about, as it is moved, in various directions; but it differs from the opal in all other particulars, especially in its want of the great variety of colours seen in that gem, and in its superior hardness. It is usually found between the size of a pea and the breadth of a fixpence; is almost always of a semicircular form, broad and flat at the bottom, and rounded and convex at the top; and is naturally smooth and polished. It has only two colours, a pale brown and a white; the brown seeming the ground, and the white playing about in it, as the fire colour in the opal. It is considerably hard, and will take a fine polish, but is usually worn with its native shape and smoothness. It is found in the East and West Indies, and in Europe. The island of Borneo affords some very fine ones, but they are usually small; they are very common in the sands of rivers in New Spain: and in Bohemia they are not unfrequently found immersed in the same masses of jasper with the opal.

ASTERIA is also the name of an extraneous fossil, called in English the star-stone. The fossils are small, short, angular, or sulcated columns, between one and two inches long, and seldom above a third of an inch in diameter: composed of several regular joints; when separated, each resembles a radiated star. They are, not without reason, supposed to be a part of some sea-fish, petrified, probably the asterias or sea-star. The asteria is also called astreites, astroties, and astereicus. They may be reduced two two kinds: those whose whole bodies make the form of a star; and those which in the whole are irregular, but are adorned as it were with constellations in the parts. Dr Litter, for distinction's sake, only gives the name asteria to the former sort, distinguishing the latter by the appellation of astroties; other naturalists generally use the two indiscriminately. The asteria spoken of by the ancients, appears to be of this latter kind. The quality of moving in vinegar, as if animated, is scarce perceivable in the astroties, but is signal in the asteria. The former must be broken in small pieces before it will move; but the latter will move, not only in a whole joint, but in two or three knit together. The curious frequently meet with these stones in many parts of England: at Cleydon in Oxfordshire they are found rather larger than common, but of a softer substance; for, on being left a small space of time in a strong acid, they may easily be separated at the joints in small plates.