Grading Ammolite
Ammolite Canada follows a grading system to maintain consistency. Whilst the ammolite industry does not have a universal grading method, we grade gemstones based on the system used by the International Gem Society (IGS).
This system grades based on factors such as colour, iridescence, chromatic shift and the rotational range of colour. The highest grade of ammolite in this system is AA, followed by A+, A and A-. Some other companies describe the highest quality of ammolite as ‘AAA grade’ but this is not a grade according to the IGS standards. Therefore, it is not used by Ammolite Canada to describe top-quality ammolite.
What makes a top-grade ammolite gemstone?
To achieve AA grade status, an ammolite gemstone must meet specific criteria.
It has to have at least three colours: one from the blue, green and red family. Orange and yellow shades are categorised under the red group and purple is included within the blue. The percentage of each colour can also determine the value of the gem. For example, a greater percentage of purple can increase the value as it is the rarest colour.
The stone must be naturally bright and have no dark areas.
The stone must have spectrochromatic shift. This is when the colours of the gemstone shift through the entire spectrum depending on the viewer’s perspective and the angle of light. Lower grade gemstones may show dichromatic shift, when blue will shift to green for example. Some ammolite material will just show monochromatic shift, where the colour shift remains within the same colour family, such as different shades of red.
Vibrant colour must be visible through 360 degrees of rotation. Lower quality gemstones may show a decrease in brightness when rotated, where the colour darkens or turns to black. This occurs due to natural inclusions in the ammolite which block the light.
Ammolite Canada only uses high-quality ammolite for our jewellery pieces, mostly of AA or A+ grade.