Aurora has recently adopted a new grading system based on the above grid. Stones with three colors, and high brilliance are graded as AAA, two colors AA, one color A, and so on, depending on color play and brilliance.
The reason for the change is that the new system is more practical and understandable to the general public, and consequently, easier to use. A more detailed description, with color samples, will be posted in the near future.
The system below is now obsolete.
Ammolite is classified into the following grades:
Reserved for the only the best stones, which display intense brilliant multidirectional fire with an even spread of at least three vivid colors.
Bright vivid color which may contain minor inclusions. Three colors with a less even spread, or two very distinct and vivid colors with little or no directional extinction.
Strong fire of two or more colors (usually red, green), clean and vibrant. Shows color from many angles.
Good color, less vivid and/or bright (typically reddish orange and green). Also referred to as standard grade.
Colors are faint or less distinct. Less play of color and more directional extinction (colors may fade or disappear as the stone is rotated).
Nature doesn't make perfection.. it makes excellence ( a line borrowed from my old gemmology instructor). A good quality ammolite stone should be bright, no matter what the color. Ammolite is found in all the spectral colors. Reds and greens are most commonly seen, with pure blues and purples being more scarce, and consequently higher priced. Ammolite triplets may show some slight feathering or inclusions, which do not necessarily indicate a weakness in the stone. Perhaps more signifigant is the degree of directional extinction, or, in other words, the stone's tendency to fade, or lack color from certain directions. The picture on the right illustrates this effect, as the same stone is rotated. When this effect is pronounced, it detracts greatly from the stone. Reflective brilliance, range of color, visible flaws and directional color extinction all play together in varying degrees in every stone, to create an overall impression of quality.
As ammolite encompasses so many types and varieties, and colored stone grading has historically been as much subjective art as objective science, standard grading is difficult. In general, our system works for most stones, however some ammolite is difficult to categorize. A stone which displays an uncharacteristic flaw or blemish, which detracts slightly from the overall look, is downgraded by one category. Stones which cross the threshold of two categories are graded to the lower one.
We recommend that you deal only with established, reputable dealers. If you have perused the various sites that advertise this gem, you may notice some wide discrepancies in pricing and grading systems. You may also see pictures of one grade, while being offered a different grade in the merchandise for sale. For this reason we have illustrated grading samples for your reference, and they are typical of what you can expect from Aurora Ammolite Mine. Our products are unconditionally guaranteed against separation.