Cyriac Ring

This little Sunstone sparkles in it's Argentium Sterling Silver Setting.  It is a size 7.5.

The name "sunstone" is used for specimens of translucent to transparent feldspar that produce bright metallic flashes when light interacts with tiny plate-like mineral inclusions within the stone. These mineral inclusions usually have a common orientation, and light entering the stone reflects from them at a common angle. This produces a flash of light in the eye of the observer who views them at the proper angle. This optical phenomenon is known as "aventurescence."

The first materials to be called "sunstone" because of their aventurescence were specimens of oligoclase, a plagioclase feldspar. As other types of feldspar with a strong aventurescence were discovered, the name was also applied to them. Labradorite feldspar (another plagioclase) and orthoclase feldspar have both been found with strong aventurescence. 
http://geology.com/gemstones/sunstone/