The sapphire-spangled emerald is long and weighs . Both sexes of all subspecies have a medium length straight bill with a blackish
maxilla and a pinkish to horn colored
mandible with a darkish to blackish tip. Males of the
nominate subspecies C. l. lactea have golden- to bronze-green upperparts with bronze-green crown, neck, and flanks. Their throat and upper breast are glittering violet-blue, the center of their lower breast white, their belly grayish, and their undertail
coverts whitish with brown streaks. Their central tail feathers have shining green or bronzy green bases that darken to the end and their outer tail feathers are bluish black. Adult females are similar but have a grayish throat with glittering turquoise spots and their outermost tail feathers have grayish tips. Juveniles are similar to adult females but with much grayish on their underparts. Males of subspecies
C. l. zimmeri have a smaller patch of glittering violet-blue than the nominate; it does not extend from the throat onto the breast. Females have a whiter throat and belly than the nominate. Males of
C. l. bartletti have a brighter green crown than the nominate, a grayish fringe on the throat feathers, a greenish center to the belly, a grayish lower belly, and much brown on the undertail coverts. Females resemble the males but are duller. Their throat and breast have white and gray flecks and their belly is whiter than the nominate's. ==Distribution==