14k white gold ring 6.5 mm round 1.5 carat Chatham created Alexandrite and lab-grown diamond .09 ctw. Emerald by day. ruby by night. alexandrites are a rare variety of the mineral chrysoberyl that changes color from bluish-green in daylight to purplish-red in incandescent light. chatham is thrilled to make this rare gem available for people who have always wanted one at a more affordable price over mined.