Custom Cut Polished Jasper Necklace/Pendant/Slide/Enhancer With Adjustable Cord  size: 1  x 13/16 inch or 25mm x 21mm 

A doublet is a gemstone that is composed of two parts; usually valuable gemstone material in combination with other, less expensive material. And a couple are Intarsia cabochons: Traditionally Intarsia pieces have a flat polish, but more contemporary pieces are more freeform and have a dome polish, and are often referred to as “composite cabochons.” Intarsia is a high expression of lapidary art requiring close mastery.