Vintage Pair of South Sea Cultured Pearls Earrings. 1980's Here is a pair of 18K white gold Stud Earrings made with two genuine cultured Australian pearls. Pearl size: 10,7 millimeter, pearl shape: round, Pearl luster: excellent. Surface: 99% clean. Stud hallmarked 750 within a lozenge which is the standard mark for 18K gold. South Sea pearls are generally much larger than other pearl types and have a unique luster quality – a soft reflection due to the large aragonite platelets that make up the pearl. They also have the thickest average nacre of all cultured pearls. These factors make South Seas both distinctive and valuable. South Sea pearls have the highest value and command the highest prices of all types of pearls. Their large size, limited culturing area, and extended growth period all combine to make South Sea pearls the rarest of all pearl types.