Guest Author - Susan Dorling

G

GIA
The Gemological Institute of America, or GIA, is recognized as a top authority on grading gemstones.

Girdle
The narrow band around the widest part of a diamond. The setting in a piece of jewelry usually grasps the diamond around the girdle.

Grade
Gemstones are frequently sent to an independent laboratory such as the GIA, AGS, NGL, or AGTA to be graded against a master set of gemstones, according to an industry-wide common set of grading guidelines. These grades are compiled to form a complete appraisal which offers an assessment the worth of a gemstone.

H

Head
The part of the setting that holds the center stone or solitaire in place.

Hardness
The part of the setting that holds the center stone or solitaire in place.Moh's scale of hardness is useful for comparing the relative hardness of different gem materials. The values are as follows:

• 10 – Diamond (hardest)
• 9 – Corundum
• 8 – Topaz
• 7 – Quartz
• 6 – Feldspar
• 5 – Apatite
• 4 – Fluorite
• 3 – Calcite
• 2 – Gypsum
• 1 – Talc (softest)

Head Shape
The shape of the head, which is determined by the shape of the gemstone the head holds. For example, the head that holds an ideal-cut diamond is round, where as a head that holds a princess-cut diamond is square.

Head-size Range
The range of carat weights of gemstones that can be mounted into a particular head.

Hue
A term used to describe the attributes of a gemstone's color.

I

Inclusion
The trace minerals, fractures, and other imperfections that contribute to the unique fingerprint of a gemstone. All but the rarest gemstones contain inclusions, which are created during the gemstones' formation in the earth.

IGL
The Independent Gemological Laboratories, Inc. or IGL. This group is recognized by the jewelry industry as an authority for grading gemstones.

L

Luster
A combination of the pearl's exterior shine and glow from within. Luster is created by light reflected from tiny crystals in the nacre.

M

Matinee Length
A pearl necklace 24 inches long.

Millimeter
The unit of measure used to determine a pearl and gem's diameter, equal to about 0.04 inch.

Mohs hardness scale
A scale developed by Friedrich Mohs to determine the relative hardness of minerals and other objects. The scale assigns the numbers 1 to 10 to specific minerals, softest to hardest respectively, using a scratch test.

Mother-of-Pearl
The iridescent lining of an oyster shell, often used as a nucleus for a cultured pearl.

Marquise
A stone cut in a boat shape, pointed at both ends, with rounded sides. Note that the correct pronunciation is "Mar-KEYS", not "Mar-KEY" which is commonly heard.

Mine Cut
A style of diamond cutting popular before 1890 or so, it features a cushion shaped outline, rather than the round outline of the modern cut and old European cuts, and has a different facet arrangement.
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