Tanzanite Color Grades: Understanding “VB 6/6”

Using the GIA (Gemological Institute of America) colored stone grading scale, fine tanzanite is typically graded around 5/6—a rich, vibrant color that is highly valued and widely admired.

At the very top sits the rarest material, often referred to as “investment grade” tanzanite. Graded 6/6, these exceptional stones make up less than 1% of all production and represent the finest color the gem can offer.

How the GIA Colored Stone Grading System Works

The GIA grading system evaluates gem color based on three components:

Hue: This reflects the basic colors we perceive. When discussing a gem’s “color,” most people refer to its hue.
Tone: This indicates a gem’s relative lightness or darkness on a scale from 2 to 8.
Saturation: This describes the hue’s intensity on a scale from 1 to 6.

For instance, a tanzanite graded as “vB 6/6” means:

Hue: Violetish-Blue (vB) – Blue dominant, violet secondary - more than 50% blue under white light.
Tone: 6 – Medium Dark
Saturation: 6 – Vivid

HUE – Blue or Violet Dominant?

“Blue dominant” (vB) means the stone appears more than 50% blue when viewed under white light.

Even in blue-dominant tanzanite, flashes of violet are still visible due to its natural pleochroism.

In gemological reports, color is written using abbreviations: the primary color is capitalized, and the secondary color is lowercase.
For example:

vB = violetish blue
bV = bluish violet

Important Facts

It’s important to note that the GIA does not issue Gemological Reports stating a tanzanite’s colour grade. They simply state whether the stone is blue or violet dominant.

You can see on the GIA certificate below that the colour is described as “violetish blue.” This means the stone is predominantly blue — more than 50% blue as its main colour — with violet as the secondary colour. But we cant tell from the certificate how dark or light the color is.

Lighting Matters

Tanzanite is graded under ONLY white light. Your stone WILL change color under different lighting conditions – and some stones can be very “moody” or exhibit very different colors in different lights. Yellow light makes your stone more violet , and white light more blue.

Buyer beware! If you're looking for (or have been promised) an intensely saturated blue tanzanite weighing less than 2.50 carats with a vb 6/6, you may be in for a disappointment. A fine, 1.00-carat tanzanite is likely to be at most a medium blue, or GIA 5/5. Be cautious of online retailers selling smaller stones (between 0.50 and 2.50 carats) as “investment grade” or GIA 6/6 !

Written by Linda Kennedy