Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
gemmārĭus, a, um, adj. [gemma], of or pertaining to gems: ars, Vulg. Exod. 39, 6 and 29.
Hence, subst.: gemmārĭus, ii, m., a jeweller, Inscr. Orell. 4302; cf. ib. 2661; Inscr. Murat. 941, 2; Vulg. Exod. 28, 11.