Stacking Rings; the series concept.
Because this series is modular in concept, the choice of options is enormous. This is particularly so with the multi-stone versions. The examples on this page have an Opal as the major stone. This can be a crystal Opal cut into an oval of marquise shape. Alternatively it could be a boulder Opal which is a layer of Opal material still attached to a fragment of the substrate rock on which it was originally formed. These tend to be cut into free-form shapes.
Stacking Rings; with Opal:
Whilst Opals require great care, their popularity as a semi-precious stone has been long lived. Some regard opals as harbingers of bad luck. This notion, according to Wikipedia, seems to originate from an incident in a novel by Walter Scott written in 1829. In this book, the death of a baroness was attributed to the wearing of an opal. This superstition, surprisingly, still lingers on. However, for most people, opals are a mysterious and beautiful gift of nature.