There are a possible 134 Malachite gems in the game (see that section of the DKS FAQ/Guide
), though that is much more theoretical than practical. I did a moderate amount of reloading and got 2 or 3 gems per malachite vein; in FoV for any quest that gave more than one choice of reward I reloaded up to 3 or 4 times (usually) to see if the sets of gems would come up malachite (side or minor quests could have 2 gems in the random loot, while some of the main quests could have 5).
I played a warrior in D2:ED (original release) and Ranger in DKS, which I found fun, though for the ranger I had to stop distributing stat points after level 15 to keep things challenging. I don't usually play mage characters, though, so for my next game (eventually) I'm planning on starting an unarmed warrior.
In DKS magic spells get a bonus from magic damage weapon bonuses and enchantments, so for best effect mages should duel wield (no need to boost the associated skill, as the off-hand penalty is not applied to spells).