A grading system is used to maintain consistency. The Ammolite industry has yet to decide on any one grading system, however overall most systems refer to colour, brightness, play of colour, and inclusions.
The grading system used at the Ammonite Factory is from the International Gem Society (IGS). Grading is used to determine the value of the Ammolite gem. Of course, Ammolite can hold an inherent beauty that appeals to the person who observes it, regardless of the grade.
Primary colours are red, green and blue. When looking at an Ammolite gem you can see various shades of these primary colours, you could possibly see indigo, violet, pink, emerald, lime, turquoise, teal, orange, cherry, raspberry, or others. The percent of each colour can also determine the value of the gem. For example; the greater the percent of purple can increase the value because purple is the rarest color. See below for examples of graded Ammolite.
As the electron micrographs show to the right, it appears that layers of blue Ammolite are more tightly packed together than layers of red or green Ammolite. Between these stacked layers are fracture fillings that act as structural support for the aragonite. Blue Ammolite would therefore be more fragile than the stronger red layers. This information is congruent with experience with fossil restoration, as red stones are usually thicker and tougher and blue or purple stones are thinner and can break easily.
AA - Top Grade Gem - Bright vivid colours - 360 degree rotational range with a spectrochromatic shift. It has to be brilliant and it has to have three or more colours present, with very few inclusions. Usually only found in the blue zone when mining.
A+ Grade Gem - Reflects light brightly, with distinct colours, has predominantly one or two vivid colours with dichromatic shift and a 240 degree rotational range of color, it can have some inclusions.
A Grade Gem - Definite patches of colour, Usually only one colour or variables of one colour (monochromatic) or pale or dark. Or it can have many inclusions, rotational range of colour is 180 degrees. So some colour extinction occurs. Usually occurs in the K zone of mining.
A- Grade Gem - Less brilliant colours overall - dull or dark- fragmented look when rotated under the light- 90 degree rotational range. Little chromatic shift. Many inclusions.