79 00 ct wonderful dual color alexandrite gemstone cushion cut jewelry making loose gemstones alexandrite hydro gems dual color loose gems thediamondexporter. This 2 42 carat naturalalexandrite cat s eye cabochon gemstone has a fine color change from rich dark bluish green in daylight see left side of photo at left to a dark grayish purple color under incandescent light as shown in the right side of the photo at left alexandrite is a rare chrysoberyl variety with color change under different kinds of light. The largest cut alexandrite gemstone weighs 66 carats and is currently located in washington d c s smithsonian institution.