The "radiant" is a special cut for diamonds. This cut is derived from the brilliant cut, but has more facets than the brilliant cut usually has. Developed by an American named Henry Grossbard, the radiant cut has exactly 70 facets, which give it its characteristic appearance.

Rhodium plating is a process by which the surface of a piece of jewelry is coated with a thin layer of rhodium. Closely related to platinum, rhodium is a very hard metal with a clear white glow. Rhodium is used to give a fresher look to the often grayish shimmer of white gold alloys. The rhodium layer also often serves as a protective coating: for example, for silver objects, because rhodium does not oxidize. Rhodium plating is applied to jewelry after it is immersed in a galvanic bath.

Rhodolite is actually a pyrope , but it was given a proper name because of its characteristic pink-red color. Pyrope belongs to the garnet group and was a fashionable stone in the eighteenth and nineteenth centuries. The name "rhodolite" is also sometimes used to describe rose-red almandines.

The river is an old term that was previously used to assess the quality of diamonds. "River" is a term used to describe the color of a diamond. "River" is the highest level in the color scale and corresponds to "highly fine white". In the international recognized color scale of the CIBJO, this level of quality is divided into "highly fine white" and "highly fine white" and is labeled with the letters "D" and "E". The next lowest quality levels are Top Wesselton ("fine white") and Wesselton ("white").

Many diamonds joined in a long row, separated but flexibly, connected to each other, create an extraordinarily luxurious and sparkling bracelet or necklace. This is how the name of this technique for setting diamonds originated: "Rivière" is the French word for a river or a flowing mass.

Rubellite is a variety of tourmaline. It occurs in colors ranging from pink to red, sometimes with a purplish tinge. Depending on its hue, a rubellite can also be described as a "red tourmaline" or a "pink tourmaline".

Ruby received her name because of her color: the Latin word "rubens" means "red". One of the most precious gemstones in the world, a ruby can often be much more valuable than a diamond of equal size because immaculate rubies are extremely rare. The most avidly sought after stones come from the mines of Mogok (Burma) and have a unique color called "dove's blood" - a special shade of red covered with a puff of blue. Thailand, Sri Lanka, and Tanzania are important sources of rubies. It was not until 1800 that ruby was recognized as a member of the corundum group. Before that date, the word "ruby" was also applied to red and garnet thorns, otherwise all three were simply called "carbuncle stone". In the past, ruby was considered a symbol of power, courage and dignity. During the Middle Ages, it was widely believed that a ruby would darken whenever bad luck or misfortune was imminent.

The rundist, often also written "rondist", is part of a cutting of precious stones. It includes the belt that surrounds between the top and bottom of the cut. On a brilliant-cut diamond, the facets that are immediately adjacent to this separation belt are called "upper rondist facets" and "lower rondist facets". These are followed by the main facets and the table (on the upper side) and the dot or culet (on the bottom side).

Highly refractive rutile has colors ranging from reddish brown to blood red and black. Although the stone has an almost metallic glow, it does not play as important a role as a jewelry stone. Rutile has a relatively low hardness. This mineral, however, occurs as inclusions in a variety of gemstones. When it occurs as an inclusion, rutile typically appears in needle-like or hair-like shapes that create beautiful patterns and amazing lighting effects. Rock crystal and smoked quartz sometimes enclose delicate straw-yellow needles or rutile fibers known as "Venus hair." Stones containing such inclusions were eagerly sought after in ancient times.