This is a beautful 5-sided cabochon of Russian Skarn. It is a beautiful combination of white and green, and the pattern is well set off by the 5-sided shape.
Skarns are calcium-bearing calc–silicate rocks, and are most often formed at the contact zone between intrusions of granitic magma bodies and carbonate sedimentary rocks such as limestone and dolostone. Hot fluids rich in silica, iron, aluminium, and magnesium mix in the contact zone, dissolve calcium-rich carbonate rocks, and convert the host carbonate rock to skarn deposits.
Although this is a cab, you can also glue on "bails", or have the piece drilled to accept a pinch bail. Either approach will let you turn this sample into a fine pendant.