RING in 750 gold (18 KT) of Art Deco style two diamonds of 0.30 carats in the center and green SAPPHIRE and calibrated DIAMONDS

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.
Sapphire : Sapphire is a gemstone of the family of the mineral corundum. The most famous color for Sapphire is blue, but trace amounts of other elements can give yellow, purple, orange, or greenish sapphires. In the case of chromium impurities in corundum it would be called a called a Ruby. Sapphires are found in Sri Lanka, Myanmar or Australia.
Carat : The carat (ct) is a unit of mass equal to 2 g. Carat is used for measuring the weight of gemstones.