January	February	March	April
Garnet	Amethyst	Aquamarine	Diamond
May	June	July	August
Emerald	Pearl, Alexandrite	Ruby	Peridot
September	October	November	December
Sapphire	Opal, Tourmaline	Topaz, Citrine	Tanzanite, Zircon, Turquoise

Coloured Gemstone Grading

Colour Gem Grading & Valuation
Comprehensive color grading is an extremely important factor in determining the value of coloured gemstones. Unlike diamonds, where the cut is one of the most important factors, the "colour" of coloured gemstones such as emeralds, rubies, sapphires, and tanzanite can influence as much as fifty percent of a gemstone's value.

Gemstone Colour Grading Basics
Gemstone colour grading is broken into three quantifiable categories: intensity (saturation), hue (colour), and tone (lightness/darkness). The GIA specifies and labels up to thirty one gemstone hues. The "hue" is the actual "colour" of the material (blue, green, red, etc.).

Gemstone Hue Chart

The GIA nomenclature also specifies six levels of saturation ranging from "grayish" (neutral grey) to "moderately strong" to "vivid." The term "intensity" is also used to describe a stone's saturation.

To describe the darkness or lightness of a coloured stone, the GIA system has nine levels of tone ranging from "very very light" to "very very dark." A numerical value is assigned to each label for use in a grading report.

With the exception of hue, each of these parameters by themselves are relatively meaningless and they must be used in conjunction to tell the full story of a gem's colour quality. Taken together, these three parameters will provide a simple numeric code that can quickly and accurately quantify gemstone colour.

Using a Kashmir or Cornflower blue sapphire as an example, in order to receive a 10 quality rating, the stone would posses a "violet/blue" hue, with a 6 or "medium dark" tone and 6 or "vivid" saturation.