The Stonecore is one of two level 82-84 instances. This one is located in Deepholm right on the side of the Temple of Earth. I tanked this at level 83 after I had secured a staff upgrade from questing in Deepholm, and had the quest from Therazane to complete. Rurikhan has posted a video for tanking The Stonecore as a Warrior, but the it's a worthwhile watch. Sword and Board have another great cheat sheet which covers The Stonecore and The Vortex Pinnacle.
The trash is pretty fine actually, with the exception of the Stonecore Sentry which will summon more mobs from nearby, so must die quickly. The Stonecore Bruisers also patrol around and in the trash at the end, you need to be careful to pull them individually while not fighting trash packs. At one point, I ended up with two of these plus a whole trash pack on me, and predictably died.
The Crystalspawn Giants do an attack called Quake which, if you are on the ground when it goes off, does 21k nature damage to you. On normal this can be ignored pretty much, but on heroic its 51k damage, so it is best to practise jumping so you are mid-air when Quake goes off.
Corborus is the first boss, a giant gyreworm. This is a 2 phase fight, in phase 1 he is above ground and will occasionally send ping shards/spikes onto a player, like Archavon in VoA. I didn't get these shards as the tank, so it may not be something you need pay attention to. There is also a debuff the healer needs to clear. The phase 1 is very much tank and spank.
Phase 2 is when he burrows under the ground, and lots of little adds appear. These should be tanked as best you can, Swipe and Thrash show their weakness here but them and Demo Roar are better than nothing. The adds don't seem to do enough damage to warrant obsessive tanking, but its better to try to get them than do nothing. The other thing is that Corborus will put an earthquake effect on the ground where he is going to appear, get out of that effect or take damage.
He has no loot for Bears as such, and only Key to the Endless Chamber for cats.
Slabhide is a big dragon you face at the end of a run down, where spikes will drop from the ceiling. Just step out of the shadows and they will miss you. The boss himself does not a lot.
Keep him faced away from the party so his Sand Blast misses them. The earth will shift where he will summon lava pools, just keep out of them. He will fly into the air and drop loads of the spikes down on the ground, just avoid standing in the shadow and you will not get hit. However, these spikes block line of sight, so you need to figure out where your healzor is and make sure they are in LOS. I managed to get out of LOS at some points, so popping a cooldown like Barkskin will mean you don't drop health too much.
Other than those abilities, this is a tank and spank. He doesn't drop any tank loot but does drop a mount apparently on both modes.
Ozruk is a giant stone guy who has gone a bit mad, so Therazane reluctantly asks you to kill him. He has a number of abilities which tanks need to practise avoiding and are probably lethal on heroic mode.
First up is Ground Slam which does a lot of damage, so you must avoid it. It is a 3 second cast, so is quite difficult to avoid. The advice on Wowhead is to run between his legs - he stands still while casting and I assume you then run back again. Missing this isn't totally deadly but it can take half or more of your health. I strafed round 90 degrees to his side, which also worked to avoid the effect.
His second ability is Shatter which on normal you get no warning for, however it is only 31k damage, so you probably don't even need a cooldown and can just eat it.
Notable loot is the Pendant of the Lightless Grotto which would be very nice with the crit strike reforged to dodge.
High Priestess Azil
This humanoid type does a few interesting abilities and is a 2 phase fight. She will do a force grip and grab the tank, slamming them into the ground for 20k damage. This can cause threat issues if you are trying to get a lead on her, so Berserk is handy to catch up again here. The force grip can apparently be interrupted, but it is on a 1 second cast, so it's unlikely it will be. As it only does 20k damage the biggest problem is that you can't generate threat while gripped.
A more interesting ability is that she places gravity wells on the floor, which are like big black holes. These will suck players in and do damage if you get too close, so avoid stuff on the ground again.
There are adds who rush to her aid at several points during the fight, these are weak and only have 10k health so I found the DPS were able to kill them by themselves. However they can be damaged if they run through the gravity wells, and keep an eye on your healer at least, who will appreciate being saved from the adds.
In phase 2 she casts a shield, becomes undamageable and stands on the platform. During this phase the tank just tries to pick up the adds, and everyone avoids the big boulders she throws at you.
The fight alternates between phases and eventually she is dead, dropping Darkling Staff and Helm of Numberless Shadows and Leaden Despair looks interesting.
The Stonecore is a nice instance, very linear but on normal it is pretty easy, despite being a level 83 instance and therefore I assumed a "proper" challenge.