Page:A treatise on diamonds and precious stones including their history Natural and commercial.djvu/183

 of opal has lately been imported from Mexico, in considerable quantities. It is pellucid and so soft that it may be scratched by the knife. Some specimens have brilliant patches dispersed in an earthy substance; these appear to great advantage after having been submitted to the process before described.

that has been long exposed to the action of the atmosphere, especially in stagnant waters, often becomes beautifully opalescent, and presents a richness of color equal to that of the gem itself. The cartilage of the hinge of the Chama Gigas, after desiccation, bears also a striking resemblance to the most beautiful varieties of opal, for which, as wellas the preceding, it has sometimes been sold. These imitations may generally be detected by their inferiority in hardness.