The color-suite of the mineral is much more extensive and varied than has been generally admitted by mineralogists. We are led to infer from their works that white is the prevailing hue of the gem; but Beudant declares that perfect limpidity and whiteness is rare comparatively, and that the stone is generally affected with yellowish or brownish tints. But what becomes of the vast numbers of these clouded or tinged and inferior gems, if the mines yield so many of them in comparison with the snow-white? Are they consumed in polishing others, or expended in the arts, or have the lapidaries secret processes by which these objectionable tints are expunged from the stone? Barbot, the French jeweller, declares that, by means of certain particular and energetic agents, aided by a proper degree of heat, he is able to remove the greens of all shades, the light-red, and the yellow, when the coloring matter is superficial, or even situated between the external laminæ. We are inclined to believe Barbot in this particular reference, especially as he admits that he is unable to change much the deep-yellow, the brown, and the smoky-tinted stones. Of the yellow tints, the diamond affords the most beautiful examples, and far surpasses in variety all the other gems, with the exception perhaps of quartz. To the yellow topaz it is decidedly superior in its range of shades, and in some of its chrome-like tints it is without an equal among the gems. This hue of chrome mixed with a faint tinge of green is a delicate, yet gorgeous, shade, and is not often seen. Stones of a canary-yellow are quite common, and perfect resemblances to the Brazilian topaz are not rare. From these hues they pass insensibly into brown and black. The transparent light-brown stones are often modified in hue when exposed to the action of heat, and some of them exhibit remarkable changes of color. M. Halpen, in 1866, exhibited to the French Academy of Sciences a singular diamond of this description. It was a stone of sixty grains weight, and of a whitish hue tinged slightly with brown. But when it was exposed to the action of heat it changed its tint to a fine rose-color, and retained it for six or eight days, when it gradually returned to its natural hue. This remarkable effect was not an accidental result, but was tried five times at the Academy with success and without injury to the stone. In other colored diamonds the action of fire often produces permanent effects, and sometimes a brownish hue is converted into a decided red color. Buckman saw a diamond with a large brown spot in its interior change to a beautiful red, like that of the Balais ruby, after the stone had been placed in borax and exposed to a red heat. Another stone, however, of similar appearance, likewise exposed, changed to a permanent black, to the great injury of the gem and dismay of the experimenter. The red varieties of this mineral are rarely of deep tints, but when they