Page:A treatise on diamonds and precious stones including their history Natural and commercial.djvu/151

 SECT. VII.

''Amethyst, Yellow Crystal, Rock Crystal, and Cat's Eye, Sard & Onyx, Opal, and Chrysoprase.''

substances belong to the same class, and differ chiefly in color and translucency. The color of the Amethyst, when perfect, resembles that of the violet or purple grape; but it not unfrequently happens, that the tinge is confined to one part of the stone only, while the other is left almost colorless. When it possesses a richness, clearness, and uniformity of hue, it is considered a gem of exquisite beauty; and as it occurs of considerable size, it is suited to all ornamental purposes.