Ring in 18 carat white gold (750/1000) decorated in its center with a large tanzanite cabochon of around 15 carats surrounded by tapered diamonds

Grey gold : Grey gold is obtained by adding silver, manganese and copper in specific ratios to the gold alloy.
Cabochon cut : Means a polished dome shaped gemstone stone, without facet.
Color : White diamonds color range from D (colorless, the purest white) to Z (light color). D, E and F are colorless diamonds, G, H , I and J are near colorless , K and L are faint color, M to Z have a light color.
Diamond : In mineralogy, diamond is an extremely rare, precious and hard (named after the ancient Greek "unbreakable") metastable allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice.