Diamond is the only stone that has a universal grading standard. All other precious and semi-precious stones are graded by eye based on industry experience and personal preference. Most tumbled stone producers only produce one grade of stone, which is whatever quality the factory owner considers to be acceptable. The world’s leading producer of tumbled stones divides their stock into two categories. Unsorted (sometimes called “D” or “C” quality) and Hand-sorted. Hand-sorted tumbled stones may be further sorted into B, B+, A-, A, A+, AA, AA+, and AAA.
Moonrise Crystals only sells crystals that can be categorized as A, AA, and AAA.
Grading is determinized by a combination of factors:
Color
Stones with a vivid and pure color receive higher grades. Ideally, the color should look attractive in all lighting conditions. If the stone has colorful patterns, they should be distinctive rather than muddied.
Clarity
Transparent stones are typically graded higher than opaque stones. Clarity is eye-grade and can be assessed without magnification. For dark-colored stones, the transparency may only be observed when the stone is backlit.
Iridescence & Prisms
Stones that have a strong iridescence receive higher grades. While clarity is valued, attractive inclusions that create rainbow prisms may also contribute to a higher grade.
Polish
In general, polished stones should be smooth. But depending on the hardness of the stone, the matrix it grew in, and the type of polishing it received, the stone may have scratches or cavities. It is unrealistic to hold tumbled stones to the same polishing standard as jewelry-quality stones.
Artificial Treatments
Fully natural stones will always be graded higher than treated or manmade stones. Brighter colors and iridescence can be artificially produced by irradiation, heat-treatments, dye and other factory processes.
