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Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z ALL

Canary Diamond
An intensely colored “yellow” diamond. The yellow may be very slightly greenish or slightly orangey, but it must be deep enough to be a distinct asset. Such a diamond is called a fancy.
Carat
A unit of weight for diamonds and other gems. The carat formerly varied somewhat in different countries, but the metric carat of .200 grams, or 200 milligrams, was adopted in the United States in 1913 and is now standardized in the principal countries of the world. There are 100 points in a carat. It is sometimes incorrectly spelled “karat,” but in the USA karat refers only to the fineness of pure gold and gold alloys.
Carbon
An inclusion in a diamond that appears black to the unaided eye.
Carbon Pinpoints
The same as carbon spots but extremely small and somewhat more likely to be opaque.
Carbon Spots
Any black-appearing inclusion or imperfection in a diamond. Actually, black inclusions are rare, although some may occasionally be graphite or small particles of another mineral. Although many diamond contain inclusions that “appear” black under ordinary lighting, dark-filled illumination, plus magnification, shows most to be caused by reflection from cleavages or included transparent diamond crystals or other transparent minerals.
Cavity
An opening on the surface of a fashioned diamond. It may be cause by cleavage, by a blow, or may have been “pulled out” from the surface during the polishing operation.
Certified Gemologist
A title awarded by the American Gem Society to qualified jeweler-members. To qualify, a person must study colored stones and their identification and diamond grading and appraising. Also, he must prove his proficiency with several written examinations, a diamond-grading examination, and pass a 20-stone gem-testing examination without error. This is the AGS’s most advanced title.
Champagne Diamond
A greenish-yellow to yellow-green diamond of a sufficiently pronounced hue to be an asset. Such a stone is called a fancy.
Chip
(a) A curved break on a diamond that extends from a surface edge. (b) A small rose-cut diamond or single-cut melee. (c) A cleavage piece of diamond that weighs less than one carat. (d) A small, irregularly shaped diamond.
Clarity Grade
The relative position of a diamond on a flawless-to-imperfect scale.
Clean
A term used by some jewelers to mean absence of internal imperfections only, and by others to describe diamonds with slight imperfections. It is prohibited by the American Gem Society for use by its members. It is also prohibited by the Federal Trade Commission, unless the stone meets the Commission’s definition of the term perfect.
Cleavage
(a) The tendency of a crystalline mineral to break in certain definite directions, leaving a more or less smooth surface. (b) The act or process of producing such a break. (c) One of the portions of such a mineral resulting from such a break. (d) A term sometimes used for a diamond crystal that requires cleavage before being fashioned. (e) A misshapen diamond crystal, particularly one that is flat and rather elongated. The term is used by diamond cutters to refer to such a crystal, whether or not its form results from cleaving. (f) A grading term used at the mines for broken diamond crystals above one carat, of reasonable thickness, and not twinned. (g) A break within a diamond.
Cleavage Crack
A break parallel to a cleavage plane. It is characterized by a two-dimensional nature; intersections with facets are usually straight lines. It is generally the most damaging kind of imperfection in a diamond, since it affects durability as well as beauty.
Closed Culet
A culet on a diamond that is too small to be resolved with the unaided eye and that can be seen only with difficulty under 10x. The term is rarely used to refer to a pavilion point or ridge with no “culet.”
Closed Table
A term used by some diamond men to designate a small table diameter. However, its interpretation and use varies. It may refer to a diameter less than the American cut 53% (of the girdle diameter) or, more frequently, to a table smaller than about 60%, because so many of the stones cut today have tables well over that figure.
Cloud Texture
A group of tiny white inclusions, composed of minute hollow spaces, or very small patches of tiny crystals or other impurities that produce a cottony or clouded appearance in a n otherwise highly transparent diamond. A cloud may be so minute that it is difficult to see under 10X, or it may be large enough to deprive the entire stone of brilliancy.
Cloudy Texture or Cloud Texture
A group of tiny white inclusions, composed of minute hollow spaces, or very small patches of tiny crystals or other impurities that produce a cottony or clouded appearance in a n otherwise highly transparent diamond. A cloud may be so minute that it is difficult to see under 10X, or it may be large enough to deprive the entire stone of brilliancy.
Commercially Clean
The common meaning of this term is “reasonably free from inclusions.” IF a diamond were without flaws or blemishes, logically, it would be called flawless or perfect. Sometimes, highly flawed stones are represented as “commercially clean.” The obvious misleading nature of the term has led the American Gem Society to prohibit its use by Society members. It is also prohibited by the Federal Trade Commission, unless the stone meets the Commission’s definition of the term perfect.
Critical Angle
The largest angle measured from the normal at which light can escape from and optically dense substance, and the smallest angle to the normal at which light is totally reflected within the dense substance.
Crown
That part of any fashioned gemstone above the girdle.
Cube
One of the seven basic forms in the highest symmetry (hexoctahedral) class of the cubic, or isometric, crystal system. It has six square faces that make 90° angles with one another, each of which intersects one crystallographic axis and is parallel to the other two. Gem-quality cube-shaped diamond crystals are so rare as to be regarded as collector’s items.
Cubic System
A crystallographic system, the crystals of which may be described by reference to their axes of equal length, each situated perpendicularly to the plane of the other two. Diamond belongs to this system.
Culet
The small facet that is polished parallel to the girdle plane across what would otherwise be the sharp point or ridge that terminates the pavilion of a diamond or other gemstone. Its function is to reduce the possibility of damage to the stone.
Cushion Cut
The older form of the brilliant cut, having a girdle outline approaching a square with rounded corners. Essentially an old-mine cut.


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