Though extremely difficult to analyze, the cut of a diamond has three attributes: brightness (the total light reflected from a diamond), fire (the dispersion of light into the colors of the spectrum), and scintillation (the light flashes – or sparkle – when a diamond moves).

An understanding of diamond cut begins with the shape of a diamond, with the standard round brilliant dominating the majority of diamond jewelry. All other diamond shapes are known as fancy shapes or fancy cuts and include the marquise, pear, oval, and emerald cuts. Hearts, cushions, triangles, and a variety of other new shapes are also gaining popularity in many forms of diamond jewelry

Diamonds are valued by how closely they approach colorlessness – the less color, the higher the value. Most diamonds found in jewelry stores run from colorless to near-colorless with slight hints of yellow or brown. The only exceptions are the fancy-color diamonds that lie outside of this range.

GIA's diamond color-grading scale is the industry's most widely accepted grading system. The scale begins with the letter D, representing colorless, and continues, with increasing presence of color, to the letter Z. Diamonds are color-graded by comparing them to stones of known color under controlled lighting and precise viewing conditions.

Many of these color distinctions are so subtle that they are invisible to the untrained eye. But these slight color differences make a very big difference in diamond quality and price.

Every diamond is unique. But none are absolutely perfect even though some come close, even under 10x magnification. Known as flawless diamonds, they are exceptionally rare. Most jewelers have never even see one.

The GIA Clarity Scale contains 11 grades, with most readily available diamonds falling into the VS or SI categories. In determining a clarity grade, GIA considers the size, nature, position, color or relief, and quantity of clarity characteristics visible under 10x magnification.

• Flawless (FL)
  No inclusions or blemishes are visible to a skilled grader using 10× magnification
  
  
• Internally Flawless (IF)
  No inclusions and only minor blemishes are visible to a skilled grader using 10× magnification
  
  
• Very, Very Slightly Included (VVS1 and VVS2)
  Inclusions are difficult for a skilled grader to see under 10× magnification
  
  
• Very Slightly Included (VS1 and VS2)
  Inclusions are clearly visible under 10× magnification but can be characterized as minor
  
  
• Slightly Included (SI1 and SI2)
  Inclusions are noticeable to a skilled grader using 10× magnification
  
  
• Imperfect (I1, I2, and I3)
  Inclusions are obvious under 10× magnification and may affect transparency and brilliance

This is the weight of a diamond measured in carats. As the carat weight of a diamond increases so does its rarity and therefore its price.

One carat is divided into 100 "points," so that a diamond of 75 points weights .75 carats. The carat-weight of a diamond is the easiest measurement to determine. Most importantly, two diamonds can be of equal carat-weight, but their value can differ greatly due to their cut, color, and clarity.