The gemstone diamond

Diamonds are the hardest substance on earth. They are more brilliant than any other natural gem. Their sparkling fire, durability, and rarity make them the most prized of gems.

The most popular diamonds are colorless. However, most diamonds have a light tint, usually yellowish or brownish. Yellow diamonds as of recently have gained popularity and are commonly available. Perfectly clear diamonds are much more valuable than tinted diamonds. Very rarely, diamond occurs in deep hues of red, blue, and green. Such diamonds, known as "fancies", are extremely valuable.

Diamonds are the most lustrous of true gems. They have a brilliant luster, and also exhibit dazzling color flashes known as "fire". This is caused by dispersion, where light enters the diamond and splits into the colors of the spectrum.

Only 20 percent of mined diamonds are used in jewelry, as most are unsuitable. A flawless diamond is exceptional; even diamonds used as gems contain flaws. A grading system, instituted by the GIA (Gemological Institute of America), was implemented to evaluate diamonds based on their clarity. Three additional evaluation systems were devised by the GIA. This leads to four attributes, known as "the four C's", in which diamonds are evaluated:

Color
Cut
Clarity
Carat weight

Color
The color of diamond is graded on an alphabetical scale ranging from D to Y. This scale measures the color saturation, ranging from absolutely colorless to deep yellow (or yellow-brown). D is bright white -- not a hint any other color. Y is deep yellow or yellow-brown. The letters in-between D and Y indicate the color, depending on the amount of yellow. The bar below depicts the letter and the color saturation it represents. (The bar is not limited to yellow; it may also be yellow-brown.) The letter Z in the color grade of a diamond indicates that it is a fancy, or deep-colored diamond.

Cut
The cut, or facet of the diamond, is the manner in which the diamond is cut. The most preferred cut is the brilliant cut, a facet specially designed to bring out the most "fire" in the stone. Sometimes, this cut cannot be given, either because of flaws or cleavage habits. Other cuts are not as valuable as the brilliant cut.
Much planning must be taken before cutting a diamond, as a slight error in the facet may greatly decrease the value of the stone.

FI	Flawless	Contains no flaws or inclusions at all
IF	Internally Flawless	Contains no flaws or inclusions at a magnification of 10x
VVS1	Very, very small inclusions	Contains very tiny flaws or inclusions visible at 10x magnification
VVS2	Very, very small inclusions	Contains tiny flaws or inclusions visible at 10x magnification
VS1	Very small inclusions	Contains small flaws or inclusions visible at 10x magnification
VS2	Very small inclusions	Contains flaws or inclusions visible at 10x magnification
SI1	Small inclusions	Contains larger flaws or inclusions visible at 10x magnification
SI2	Small inclusions	Contains larger flaws or inclusions easily visible at 10x magnification
I1	Inclusions	Contains inclusions visible to the naked eye
I2	Inclusions	Contains large inclusions visible to the naked eye
I3	Inclusions	Contains very large inclusions visible to the naked eye

Carat Weight
The size of a diamond is measured in carats (abbreviated as "ct"). A carat is equivalent to 0.2 grams (about 0.007 ounces). Another weight measurement sometimes used for small for diamonds is the point measurement (abbreviated as "pt"). Each point is one/one hundredth of a carat. For example, a stone weighing 34 pt weighs .34 ct.
Larger diamonds are worth more than proportionally smaller ones, meaning a 3 ct. diamond surpasses the value of three 1ct. diamonds.

USES
Diamond is the most important gemstone in the industry. Diamonds of all different colors are faceted into various cuts; the colorless variety is most in demand. The other colors are less commonly worn in jewelry. Deep red, green, and blue diamonds are extremely rare and highly prized. Black, opaque diamond (bort) is infrequently faceted into a black gemstone with a metallic luster.

Diamond is the birthstone for April.

Bort - dark colored, imperfectly crystallized, opaque diamond. May also refer to a fragment of a gem quality diamond.

Fancy - deep red, green, blue, or purple diamond

Canary Diamond - diamond with a deep yellow color

SIMILAR GEMSTONES
Many gems resemble diamond. However, only few have a luster and fire similar to diamond. All of those, though, are much softer than diamond. Many synthetic materials are also made to resemble diamond, such as YAG, strontium titanate, cubic zirconia, moissanite, synthetic rutile, and synthetic spinel. However, diamond is easily distinguished from all the others by immense hardness. Zircon, the only natural gem that comes close in fire and luster to diamond, is softer and has a strong double refraction.