Even though by now, the OP has already decided upon choosing a 2nd prof, I am still going to state my opinion and back my statement with a rebuttal upon atomic. Again, I am not disagreeing that we can make a decent profit with the JC prof by any means (hell, I’ve done it - I have a mining/JC myself along with an herber/alchemy) but you have to look at the AH pricing and trends for your gems. Depending on wow gold, either you could make the pretty profit or in my case:

Stack of Obs = 40-55g

Stack of Ele = 60-70g

common uncut gems = 35-50g (depending on which gem) dreadstone seems to go for a bit more

Uncommon gems uncut = 80-100g

Uncommon cut - 90-120g

Stack of Twilight Jasmine = 75-90g

Stack of various other herbs = 40-65g

Now a stack of obs will grant usually 4 uncommon gems = 140 - 200g

Stack of else will normally grant 3 uncommon and 1 uncommon = 185 - 250g

Yes this is a hefty profit ranging in the hundreds however, selling the ore over gems tends to be Much faster than gems. Nearly triple favoring ore and herbs over gems some weeks. The only time it changed was during the wrath/cata transition when everyone was getting new gear and needed the gems for their new gear. I’m not even going to go into the glyph period of gold goodness but that’s a different story, good times. Then you will not need to worry your WOW Power Leveling.

Anyways, let’s take leveling up JC to 525. If you plan on farming all the mats yourself, then you won’t be spending anything to level JC but that time spent is time you could have been selling off all of your ore and herbs. Also the time you spent world of warcraft gold, the market could have totally changed for either the worse or greater.

Pros to Mining with Herbing:

Everything is 100% profit

You not obligated to crafting anything

No searching in the AH for those spare mats

Sells faster

Pretty relaxing

The extra Volatile life you can sell used by other profs

Pros to JC over Herbing:

You won’t be a flower picker anymore

You get to turn that ore into shinys (who doesn’t like shiny thing!)

You get to have 3 upgraded gems in your gear

You get to cut your own gems and save all that cheap wow gold you would have spent otherwise

JC dailys

Prospecting ore for gems and selling off the profit with cut/uncut gems

Upon upgrading a piece of gear, you probably already have the gems cut for that new piece of gear

Prospecting for others making tips

Cutting gems for others making tips

Guilds will appreciate another JC being able to cut gems for them

It all depends on what the op wants to do, if he wasn’t to spend most of his time gathering and doesn't feel like crafting anything, then the 2 gathering professions would work nicely. If he wants to go the crafting route, go with the mining/JC route and get not only the ability to save the wow items you would normally spend on gems and make them yourself and sell of what you don’t want for a proft. Not to mention you have the JC daily you can make gold off of and the better versions of gems you can put in your gear.

More games information: Guild Wars 2 gold, Tera Gold, RS Gold.