We all collect them, everyone uses them and Covetous Shen bleeds us dry when we upgrade them. The Gem article in DiabloWiki has received a complete overhaul reflecting all the changes and additions that came with Reaper of Souls. Listed are details of when and how you can get different ranks of gems, what it costs in gold and lower gems to upgrade them through all the different grades and gem properties and also there is information on socketing.
All the old gem information has been preserved as we know you like to see what it was like in ye olden days and it’s interesting to see how gems have changed over the past couple of years.
All the information should be bang up to date but if you see anything not quite right feel free to alter it, as it’s a wiki and doesn’t bite.