The monumental 22.43-carat cushion-cut tanzanite in this convertible ring displays the incredible deep violetish-blue hue for which tanzanites are so desired. The rare gemstone has been certified by the American Gemological Institute (AGL) to be untreated, meaning it has not undergone any clarity or thermal treatment to enhance its color. Found in just one place on earth, the African country of Tanzania for which it is named, the tanzanite is relatively new to the jewel market. While many…