Tanzanite: The World''s Rarest Gemstone
2021-1-21 · The system divides the gemstone into a variety of hues, ranging from bluish-violet to violetish-blue. Of more importance is the clarity grading. The clarity grading of colored gemstones is based upon the eye-clean standard. "Eye-clean" means a gemstone is considered to be flawless. Tanzanite is generally an eye-clean gemstone.