Cobalt spinel is the rarest and most valuable color variety of spinel, prized for a saturated, electric blue unmatched by any other blue gemstone — a quality driven by trace cobalt rather than the iron that colors ordinary blue spinel. This stone is explicitly identified by the lab as cobalt-bearing, not merely "intense blue," a distinction that places it in an entirely different value tier. Combined with Internally Flawless clarity — a rare grade for any colored stone — and a substantial 3.92 carat weight, this is a museum-quality example of one of the gem world's true rarities.