Mana gem concepts:
The blue mana gem has a large central crystal with a scalloped pattern bearing eight smaller crystals. I've drawn a sperical gem in some of the pictures, but for polycount reasons, it will probably be a hexagonal or octagonal cut gem in-game. The gem setting is made of dark metal, with a bright, shiny ring of silver bordering the main crystal. Around the edge of the blue mana gem are glowing blue "runes" (not authentic Viking runes, but those angular nonsense letters I make on my textures and stuff, like the examples show.) The main crystal sticks out from the setting when viewed from the side, the others don't, or do less so. Around each of the subordinate crystals are more runes/squiggles.
The green mana gem has a central green crystal the same size as the central crystal of the blue mana gem. The setting, however, is spiked instead of scalloped, with four large spikes in a spider leg configuration, and four smaller ones in a star-type pattern. Like with the blue mana gem, it has small runes/squiggles, but they're probably only on the front/back faces rather than on the sides this time.
The combined mana gem is a fusion of the blue and green designs, configured vaguely like an infinity symbol. The green mana component is on top, as it's the "higher" form of mana, and retains the larger spikes, but with the bottom pair spread to accomodate the blue gem beneath it.
And yeah, I apologize for the sloppiness, I'm painting these with my mouse seeing as my old scanner refused to work after I went to the trouble of digging it out... ~_~;