I just realized that I never actually wrote a guide on prospecting in TBC classic, which is a massive oversight, as it is literally how I made almost all my gold in TBCC.
Prospecting is the majore way you make a profit with jewelcrafting. You turn ores into the various gems in the game, and then you can cut those and sell them to players looking to fill their sockets. This is a very important part of end-game power as sockets are very abundant in TBC and the stat boosts you can get are significant.
Red gems are king
In TBC the gem colour determines what type of stats you get. Red is by far the most valuable one as it gives straight throughput increasing stats like agility, spell power and healing. The second most valuable color is orange which also has half and half stats from the red and yellow pools, with the yellow part offering stats like hit and crit that also increase damage.
This creates some very lopsided value in the results from a prospecting session and it means you have to prospect relatively large amounts of ore to be certain you are making a profit.
Adamantite versus fel Iron
There are two ore types you can prospect in TBC, Fel Iron Ore and Adamantite Ore. The rare gems are what you are after as they are the BiS option, and the drop rate is relatively low for rare gems for both ore types. Adamantite will give you rare gems at a rate of about 4.5 rares per 100 ore, whereas Fel Iron Ore is lower at 3 per 100 ore.
This ensures that Adamantite Ore Is almost always the preferred option as you get more gems and you can spend less time prospecting, which quickly stacks up.
If you want to make gold with jewelcrafting you want to get some of the gem cut recipes. This will massively increase your sale rate, as finished gems are very sought after. I would start with one of each color, and then focus on adding more for the colors you have trouble selling out of. Almost all the relevant recipes are BoE world drops, so you will just have to shell out. For red gems I would suggest going for either Delicate or Runed Living Ruby as they cover the two most in meta DPS classes in TBC classic.
Just post one of each cut you have at the time and repost frequently. Rare gems sell very quickly and there is no big issue with selling them. Uncommon quality gems however can be a real pain to sell. For those I would suggest selling a few of them as cut variants and the rest as large stacks of uncut gems. Brilliant Glass is also a way to get rid of some uncommon gems, and is likely worth it. On some realms I suspect all except the red uncommon gem will be selling for barely more than the vendor cost, if they do then just straight up vendoring is a good idea.
Prospecting is all about knowing the average yields and buying ore that is cheap enough that you can expect to profit. Calculators are the name of the game. Here’s a link to mine with the best rates I have found from old sources. Fill in the prices on your realm to get a quick overview of whether or not it is worth it. You will also need to plan to prospect enough ore that you get to roughly average results, but even with a bad first batch you will still make some gold back that you can sink into more ores until you get a living ruby or two. The variance is luckily not high enough that you should be afraid of entering.
The spreadsheet uses the Nexushub.co API, so you just need to enter the correct server slug, wich is your server name in lower case letters, with dashes between, you can see how it looks in the D1 sell for zandalar tribe. If the API does not work, simply type the prices directly into the B colum and the calculations will still work.