One time, I saw a khorium vein

Wow - is this stuff hard to farm, or what?

I was running Shattered Sun dailies with Sali, killing the demons at the portal on Dawning Square, when I saw that a khorium vein had spawned at the back of the portal. Of course, that became my first priority. I was about 50% on health and mana, and there was one Irespeaker walking near that vein. But knowing time was limited I took her on at short range. I killed her with about 10% health and mana left but immediately went to mine the vein. I was just finishing the second hit on the vein when two other miners showed up. In other words, I got there just in time.

It felt like I had won the lottery.

Alamein is a skinner, so that's been my main experience with gathering skills. There are rare leathers that you need too, but the experience is different. Take for example the [Cobra Scales]. They're skinned from a few specific snakes in Outland, found either in northern Shadowmoon or in a specific corner of Nagrand. The snakes are slightly rare and are in tough areas to farm (good number of level 70+ mobs wandering around), and the scales are only a 10% chance to drop when you skin. So you have to do a good bit of work to find them, hence they're rather rare.

Compare that to khorium. Basically, the veins can spawn anywhere in Outland, in place of a normal adamantite or fel iron vein (a 2.5% chance). If you need khorium, all you can do is travel all over and hope to get lucky. For some reason, khorium is unusually expensive on Shandris; a single ore goes for 10 to 12g. So any khorium vein that spawns will be mined almost immediately. Miners will drop whatever they're doing to get it, and will spend a lot of effort if needed.

The rarity is exacerbated because you need khorium for everything. Almost every useful high-end engineering recipe needs khorium, and I believe blacksmithing and jewelcrafting are similar. Sali needs 8 [Khorium Power Cores] for her epic flyer; that translates into 48 khorium ore. If I spend an hour mining (cruising on my slow flyer), I might find a single khorium vein.

Those Cobra Scales, for comparison, are used only for a few specific recipes. Those include Cobrahide and Nethercobra leg armors, which sell well. So the scales are useful — but there are other rare drops that are used for other recipes. For other items you might need Wind Scales or Nether Dragonscales or Fel Scales and so forth. Each drops from a few specific mobs and is used for a limited set of recipes.

The skinning flavor works quite well: specific leathers for specific recipes, farmed from a few specific mobs. This wouldn't feel as good for mining -- there shouldn't be so many variations of ores. However mining khorium shouldn't be such a crapshoot. I would add specific veins that only spawn khorium, but make them hard to reach and challenging (but possible) to farm. For instance they could spawn in deep mines in Netherstorm and Shadowmoon. If you want to clear a mine of tough mobs and wait for veins to spawn, your hard work would pay off. But at least you could do something to get khorium, rather than wait to get lucky or to pay for someone else's luck.