Lord Rhyolith, "Mr. Ankles"
Lord Rhyolith is huge. Even while on his platform, you can barely catch his face. You won't see much of this boss outside of his knees and ankles, as you'll need to keep your camera angle low to stay out of fire. Rhyolith might be massive, but your melee DPS will be beating up on his heels in order to get him to move in the desired direction. Your tanks won't bother with Rhyolith until phase 2, and so your melee DPS will be fairly autonomous. The first half of the encounter revolves around keeping everyone alive while the boss is steered into the correct positions, while the second phase will be a repeat from last week's bosses.
Rhyolith will be Concussive Stomping the ground pretty regularly, dealing fire damage to the raid and knocking back nearby players. These stomps also create volcanoes around the room. A dormant volcano isn't anything to be concerned about, and you can ignore them. The threat here is that Rhyolith can activate one of the dormant volcanoes, causing it to spew fire damage to the raid and it will start stacking the Eruption debuff on everyone. Your melee DPS will be steering Rhyolith straight into the active volcanoes, which will deactivate them permanently. Once Rhyolith has stomped on a volcano, the smushed volcano will eventually spew out some fire on the ground. As usual, stay away from the Magma Flow on the ground, and everything will be fine.
Your primary healing targets will be the tank handling the adds that Rhyolith spawns. The first type of add comes in a pack: the Fragments of Rhyolith are just grouped up and your ranged DPS classes will AOE them down. The second type of add is the Spark of Rhyolith, which a tank will handle away from the group as it gets nuked. You should be standing with the other ranged classes and healers as much as possible, as it makes AOE healing much more effective. Keep Beacon of Light on the tank at all times, as it's easy to get separated from your target if there's fire between you and the tank.
Outside of the damage that the tank will be taking from the Sparks and Fragments, most of the other damage is simply incidental. Players will be getting fire spewed on them from the active volcanoes, someone might stand in a Magma Flow, or Rhyolith can just use his Concussive Stomp to deal damage to everyone. As your raid group gets better and better at this encounter, you'll be healing less and less. You will need to be aware of where everyone is standing, as Rhyolith is on a big platform and you can easily get out of range of your targets.
I like to use Holy Light and Holy Radiance to handle healing the raid while continuing to abuse Holy Shock and Word of Glory. The tank damage on this encounter is usually not too severe, and the incoming raid damage won't be too bad if your players are good at avoiding fire. Be prepared to use all of your mana early while learning the encounter, as players without experience against Rhyolith will almost certainly end up sitting in fire at some point. You'll also have to rely on your Divine Light often while learning, as players who have made a mistake need to be healed quickly enough to ensure that the next Concussive Stomp doesn't finish them off.
Eruption puts the pressure on
The longer that the active volcanos are spewing out fire, the higher your debuff stack of Eruption will go. Eruption stacks from a long-active volcano are your biggest enemy on this encounter. If you notice that the melee DPS is taking too long to stomp a volcano, you need to take matters into your own hands. I like to use Aura Mastery to negate some of the incoming fire damage for everyone, and I'll pop a cooldown like Avenging Wrath or Divine Favor and pair it with Holy Radiance. If your Rhyolith steering crew is working smoothly and knocking down volcanoes as Rhyolith builds them, then then the fight is pretty simple to heal.
The real chaos comes from trying to handle multiple active volcanoes at once, which requires us to handle the crisis and continue healing everyone through the random damage. Toward the end of phase 1, there will be a ton of Magma Flows running all over the ground, and it can be hard to actually move. If you absolutely have to run through some fire, just be sure to use your glyphed version of Divine Protection, as the extra magical damage reduction will help ensure that you're not killed immediately. If you find yourself without any active volcanoes, you should immediately use your Divine Plea, since your incoming damage should be minimal at that moment.
Phase 2: Bloodlust and Holy Radiance time
After your melee DPS has melted off Rhyolith's armor via the active volcanoes and burned his health down to 25%, we move into the classic Bloodlust and Holy Radiance phase. The fight instantly transitions into a standard tank and spank, with the entire raid stacked up behind the main tank to facilitate AOE healing. You'll want to abuse Holy Radiance and any cooldowns you have remaining, as your tank and raid will be taking much more serious damage than they were before. The end of the Rhyolith fight is almost identical to the end of the Shannox and Beth'tilac encounters, though it still remains fairly short. Try to save up enough mana for phase 2; that way, you don't have to worry about heavily utilizing Holy Radiance and Divine Light to save lives.
The Light and How to Swing It: Holy helps holy paladins become the powerful healers we're destined to be. Learn the ropes in Cataclysm 101 for holy paladins, study the new balance between intellect and spirit and learn how to level your new Sunwalker. Tanking is a job, DPS is a craft -- but healing is truly an art.