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M

Mabe pearls - A dome shaped, assembled, pearl where plastic is placed in the host shell that nacre then grows over. These pearls are fairly inexpensive, but fragile.

Make - The term for proportions and finish of a cut gemstone. For pearls, the make relates to the match of pearls, quality of drilling and stringing of strands.

Mantle - Implanted along with a mother of pearl bead in the host oyster. Also called the nucleus, this mantle carries the cells of nacre that begin the pearl growth process.

Matinee - A strand of pearls 24 inches long.

Marquise - An oval shape gemstone with the ends cut to points.

Master stones - A set of diamonds by which jewelers can compare and grade the color of a particular stone from D to Z.

Mikimoto, Kokichi - The man who invented and, in 1916, patented, the process for culturing pearls.

Millimeter - The unit of measure used to determine the diameter and measurements of a pearl. The millimeter is also used to measure gemstones other than diamonds below ½ carat.

Mineral watch crystal - A watch glass made of mineral that is harder and more durable than glass or acrylic. Sapphire crystals are used in high-end watches.

Mixed cut - Used more for transparent colored stones than diamonds, the mixed cut simply means that the stone has both step and brilliant cut facets.

Mohs Scale - The scale that determines the relative hardness of minerals. Developed by Friedrich Mohs, the scale uses a scratch test and ranks minerals soft to hard from 1-10

Mollusk - The oyster, or other shellfish, used to produce pearls.

Mother of pearl - The lining of an oyster shell, mother of pearl is used as the nucleus bead implanted inside the mollusk along with the mantle to produce pearls.

Mounting - The method of holding gemstones in place in jewelry. Prongs, channels, etc. are mountings

N

Nacre - The crystalline substance secreted by a mollusk that coats the irritant, eventually producing a pearl.

Natural - Any pearl that is not cultured. Any gemstone that has not been color or clarity enhanced.

Needles - Long, thin, inclusions in gemstones caused by gas within the crystal.

Nucleus - The irritant imbedded in a mollusk to force production of nacre

O

Off-center culet - A major problem in gemstone cutting. An off-center culet seriously effects the symmetry of a stone.

Oiling - A common procedure for gemstone color enhancement. The treatment is not permanent and should be disclosed at point of purchase.

Opaque - A descriptive term for gemstones that are so clouded by flaws that they cannot be considered at all transparent.

Opera - A pearl strand 32 inches in length.

Orient - The iridescent play-of-color that gives pearls their deep inner glow.

Oval - A cut shape for gemstones.

Overtone - The hint of secondary color found in pearls. Typically pink, green, blue and silver