The key to getting the best light from precious gems like diamonds, emeralds, sapphires and rubies is to have the best possible cut for that particular stone, and to present it out of the setting to let the light in. That is why large diamonds are usually held in a claw setting on rings, and why diamond pendant earrings are so spectacular.
Opals and other opaque gems are often set deep into rings and polished smoothly in a ‘cabochon’ rounded cut. The many planes of a brilliant gem cut don’t do anything for an opaque precious stone, because they are intended to bring light into the stone from as many angles as possible and make the gem sparkle from the inside. Fine diamonds are of course the most precious of all gems, and it is the brilliance and internal spark that sets them apart. While the topology of brilliant gem cuts is both a precise science and a complex art, more planes and greater symmetry are considered desirable.
Earrings are the ideal way to show off clear precious stones. A tall claw that holds the stone completely clear of the metal is not really practical on most rings, both from aesthetic and practical points of view, but the task can be easily and elegantly accomplished by setting the stone in an earring. Necklace pendants are also excellent, although the light catches them less easily and unless the stone in question is very large, some kind of setting is usually necessary or it will appear quite small.
Studs are good but pendant earrings are the best option for displaying truly remarkable brilliant stones, particularly diamonds. Even diamonds of lesser calibre can be vastly improved by presentation in well designed earrings. The light enters from every angle and the gemstones will sparkle to the best of their potential.