[header] How to buy an emerald online [title] Get educated. [step] There are plenty of resources on the net, with all the how s and why s of emeralds. Here are some basics : [substeps] Basics: the four c's, as in diamonds, are applicable to emeralds as well. 
These are: color, clarity, cut and carat. Unlike in diamonds, color in emeralds is the most relevant feature.