The definition posted hints at a semitic origin, which sounds likely - one (relatively archaic) Hebrew word for emerald is izmargad (אזמרגד), a close similarity.
However, Hebrew Wikitionary claims that the word has only been in use in Hebrew since the fifth century AD, placing it after the Greek usages, and likely to have been influenced by the Greek, rather than influencing it.
The same source claims that the ultimate root for the word resides in Sanskrit marakata, or "green", which seems to be corroborated by some online Sanskrit dictionaries whose veracity I cannot evaluate:
marakata n. an emerald [ confer, compare Greek ; Latin smaragdus.]
As to how smaragdos* evolved into emerald, Etymonline gives a good overview:
Greek smaragdos -> Latin smaragdus -> Medieval Latin esmeraldus -> Old French esmeraude -> French emeraude -> English emerald.
The same source also claims that the road from Sanskrit marakata to Greek smaragdos passed through the Semitic root baraq (shine), which can be found in the other Hebrew word for emerald, bareqet, but I'm not familiar enough with the phonetic shifts between Sanskrit and Semitic languages to say if that's likely.