Mabé pearls (also known as "cultured blister pearls") are hemispherical pearls which are particularly suitable for use in brooches and jewelry for the ears. To produce them, several hemispheres of plastic or wax are glued to the interior of an oyster's shell. As the animal grows, it covers these hemispheres with layers of mother-of-pearl. To harvest the mabé pearls, the mussels are opened and the pearls removed with a milling machine. The hemispherical form is removed, the hollow space is filled up, and the flat back surface is sealed with a mother-of-pearl disk. Most mabé pearls are cultivated inside South Seas mussels of the Pinctada maxima species. The pearls grow to between 10 and 20 mm in size. Depending on the shape of the artificially inserted form, the pearls can be either oval, teardrop-shaped, or heart-shaped.

Majorica pearls are imitation pearls. They are industrially manufactured on the Spanish Balearic island of Mallorca and are considered to be costume jewelry.

Mandarin spessartine is sometimes also known as "mandarin garnet." This especially beautiful type of spessartine occurs in colors ranging from orange to reddish brown and is a member of the garnet group. Spessartine is named after Spessart, a region in Germany where it was first found. Nowadays the mineral is primarily mined in Burma, Brazil, China, and Kenya. The finest type of spessartine is a variety of mandarin spessartine found only in Namibia.

Marquise is a shape into which gemstones can be cut. The marquise cut is named after the mistress of France's King Louis XV. She loved this pointed oval shape and was particularly fond of faceted stones cut into a doubly pointed shape. A gemstone cut in this shape is similar to a navette and is likewise grouped under the main heading navette ("little ship"). A marquise diamond has a table and 56 additional facets.

The matrix is the natural stone "womb," the so-called "mother stone" in which crystals grow and in which they can be found.

Jewelers use the word "memoir" to describe very personal pieces of jewelry: rings with brilliant-cut diamonds that are presented as gifts to commemorate special occasions. The ring's endless band, which has neither a beginning nor an end, adds even greater meaning to the symbolic character of a memoir. A charming form of memoir ring is a simple and unadorned band in which brilliant-cut diamonds can be successively added as reminders of special events that have occurred in the course of one's life.

Mineralogy is the branch of science that concerns itself with the investigation of minerals. It can be divided into several subordinate parts: crystallography, i.e. the science of the form, structure, chemical and physical properties of crystals; special mineralogy, which focuses on the description of the minerals according to their genesis, external properties, and distribution; and petrology, i.e. the science of stones, which focuses on the genesis and formation of stones and the transformational processes to which they are subject. The studies of mineral deposits and technical mineralogy complete the spectrum of mineralogical subdivisions.

The Mohs' scale of hardness is named after it creator, the mineralogist Friedrich Mohs (1773-1839). The Mohs' scale arranges minerals according to their degree of resistance to mechanical scratching of their surfaces. The scale ranges from one to ten. Each mineral of a given degree of hardness is soft enough to be scratched by a mineral on the next highest level and simultaneously hard enough to scratch a mineral on the preceding lower level. Minerals of hardness 1 are the softest; those of hardness 10 are hardest. Gemstones having a resistance to scratching (Mohs' hardness) of 1 or 2 are classified as soft; gems in grades 3 to 5 are medium hard; those harder than grade 6 are described as hard. Values for all known minerals and gemstones have been determined on the Mohs' scale of hardness. The scale is used worldwide to classify the hardness of stones.

The momme is a Japanese unit of weight for cultured pearls. One momme is equal to 3.75 grams or 18.75 carats. This unit of weight is seldom used anymore in the European pearl trade. Nowadays, the weight of a pearl is typically expressed either in grains (one grain equals 0.5 grams) or carats. The latter unit is gaining in popularity.

Morganite is the pale pink to salmon or violet-colored member of the extensive beryl family. Because of its color, this mineral is sometimes also known as "pink beryl." The name derives from the American collector John Pierpont Morgan. Among other countries, the stone's principal sources include Afghanistan, Brazil, and China.

Mother-of-pearl is produced by soft-bodied animals, the so-called "mollusks." The mollusks include marine mussels and snails that have so-called "epithelial cells." These cells, which produce mother-of-pearl, are responsible for building and growing the mussel's shell. Mother-of-pearl primarily consists of calcium carbonate, a molecule which contains calcium, carbon, and oxygen. Calcium carbonate occurs in pearls in the form of aragonite, which covers the interior surface of the shell in countless thin, parallel layers or collects around a core like the skins of an onion to produce a pearl. Like a mosaic, each of the paper-thin layers of aragonite consists of countless plate-like aragonite crystals. The cement that connects these crystals to one another is a horn-like, organic substance known as "conchyne." Mussel shells made of mother-of-pearl have been used in utilitarian decoration and ornamental jewelry for thousands of years.

Pearls are particularly fascinating today because of their tremendous diversity. Never before have pearls been available in such a wide selection of different colors, forms, and sizes. Each type of pearl has its own spectrum of colors: Tahitian cultured pearls gleam in gray, silver, and black hues, often overlain with a veil of red, blue, or green; freshwater cultured pearls shimmer in white, rosé, and green, and also occur in intense red or lilac hues. When pearls of different colors are strung into a single collier, jewelers describe such necklaces as "multicolor" or "harlequin" chains. In addition to combining pearls of different colors, such chains also often combine different types of pearls.