The ruby proper is of one color, but in its varieties of intensity may change to a very light pink. When still lighter it is ranked a sapphire, which comes in almost every possible color and shade, from ruby to a perfect transparent colorless crystal. This stone differs in degrees of hardness and capacity of working--the hardest being a greenish yellow, in the shape of pebbles, with very slightly rounded edges, difficult to work, but forming the strongest and most perfect jewel known. It must be remembered that this description gives the value of the ruby and sapphire as a material for jewelling only. For ornamental jewelry, the value depending on color, of the most intense ruby or blue for sapphire, together with brilliancy and weight. The ruby and sapphire are formed on an aluminum base, the common emery being another form of structural arrangement, but of the same chemical constitution. These stones possess every quality to make them the base of perfect jewelling; and still the chrysolite is equally in favor with most jewellers. It is not quite so hard, but it is more easily worked and cheaper in price, and it would be difficult to tell wherein it is inferior to either the ruby or sapphire. It has a yellowish tinge, verging to the color of the olive. As a stone for jewelry it is not fashionable, and only in Persia is it valued. There are, however, some very strong objections to its use by the workman; it is not uniform in hardness; in polishing it will _drag_, that is, the surface will tear up in the process. Unfortunately the eye is not able to detect the fault before working, and it is found only when much preliminary time and trouble has been expended. It is susceptible, when good, of a perfect polish, and is much used in chronometer work, especially for jewelling the 4th hole, as its non-liability to fracture renders it valuable. “Aqua Marine” is a brother to the emerald, differing from it only in intensity of color, and composed of the same constituents. These two gems are the only ones in which the rare metal, glucinum, has been detected. It is extensively used in the American and English watches, but never in the Swiss. It is soft, not much harder than quartz, but comes in large pieces, perfectly transparent, and of a color which is that pure green of sea-water, from which it takes its name, “Aqua Marine.”