In case anybody missed it - the article that brought it to my attention:
Chipped -> Flawed -> Normal -> Flawless -> Perfect -> Radiant -> Square -> Flawless Square -> Perfect Square -> Radiant Square -> Star -> Flawless Star -> Perfect Star -> Radiant Star
Flawless Square is the highest that can drop, the rest have to be crafted (and are far from cheap). Each type (Ruby, Emerald, Amethyst, Topaz) has a set of properties that increase with each tier
...8 hour outage, seriously?