Greek smaragdos became Latin smaragdus. The later route includes reconstructed Vulgar Latin smaralda, Anglo-French esmeralde and Middle English emerallde before emerald.
The cards omit two intermediate stages. The Vulgar Latin form is reconstructed, not presented as a directly attested spelling.
Source
Merriam-Webster: emeraldThe noun's Word History gives the route and marks the Vulgar Latin form with an asterisk.