18K two-tone gold ring adorned with 11 diamonds of 0.02 ct in total

Gold : Because of the softness of pure gold, it is alloyed with silver, copper or palladium. The proportion of these other metals give yellow, white gold. Without precision, the gold used in jewelry is 18 K, corresponding to 75% pure gold.
Carat : The carat (ct) is a unit of mass equal to 2 g. Carat is used for measuring the weight of gemstones.
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.