Page:A treatise on diamonds and precious stones including their history Natural and commercial.djvu/161

 every one. Among the Eastern nations the opal ranks higher than in Europe.

substance is sometimes sold for black and green opal, and is often set in jewellery; it ocurs of the size of a small almond, but more commonly not larger than a lentil or pea. This precious gem is nothing more than the cartilage of the hinge of a large shell. Glass, and even scoria, having an iridescent appearance, have also often been sold for opal.