Pyrite Ore - Item - World of Warcraft
This is server dependant but in many servers you are able to make huge profit from pyrite ore.
One stack of pyrite usually gives average of 8 Volatile earth when prospected. You also get about 6 green gems and 2 rare gems.
Volatiles goes for ~25-30g in my server, green gems goes for 40-80g and rares goes for 50-200g.
Volatiles: 100-120g
Green gems: 240-480g
Rares: 100-200g.
Total: minimum 440g, maximum 800g.
One stack of pyrite costs 270-340g so you are getting pretty nice profit.
If you get those rares cut, they will give 200-400g each in my server.