Page:A treatise on diamonds and precious stones including their history Natural and commercial.djvu/158

 finest touch or stroke of the tool without chipping, and shewing the art of the engraver to the highest perfection.

stone exhibiting layers of two or more colors, strongly contrasted, is called Onyx : as banded jasper, chalcedony, &c. but more particularly the latter, when it is marked with white, and stratified with opaque and translucent lines. But the oriental onyx is considered a substance consisting of two or more layers or bands of distinct and different colors. A sard or sardoine, having a layer of white upon it, would be called an Onyx; and according to the number of layers, it would be distinguished as an onyx with three or more