When a gemstone is hard enough to polish but too soft to facet as precisely as a diamond, sapphire, or ruby, it is often fashioned into a rounded or oval cabochon, with a flat back so it sits securely in its setting. In the world of fine jewelry, agate, amber, jade, opal, and turquoise are commonly formed into big, eye-catching cabochons. Similarly, in the realm of costume jewelry, glass, paste, and plastics such as Lucite can be polished...Continue Reading