In any city, in any country, go to any mental institution or halfway house you can get yourself to. When you reach the front desk, ask to visit someone who calls himself "The Holder of Earth". The worker will laugh loudly, drawing the attention of only one other patron. The worker will remain seated, but the person whose attention he drew will call you over. Do not ask him anything as he leads you to a disused broom closet deep in the asylum. He will open the door for you and wait for you to enter first; do not do this, or the stairway inside the door will disappear and you will plummet endlessly through the ice-cold black. Instead, tell him, "I would not dare see these sights before you". If he believes you, he will nod slightly and enter, and you should follow him. If he does not, be thankful that you are deep enough into the asylum that no one can hear your screams.
As you descend the stairway, you will hear beastly yells coming from all sides, but primarily from above you. Keep your eyes trained to the darkness below you (for the man will have vanished in the darkness, though you will be able to feel that you are not alone). You must never look up, or the demons and hell spawn watching you, mocking you, will descend, rending your flesh from your bones, draining your blood, ripping your muscles and sinew in all too long of an instant.
As you climb down, you will find the atmosphere becoming more and more tomblike, and though you will still be able to hear the demons above, it will seem as though there is finally a ceiling overhead. You must still take the utmost caution never to look up. After an impossibly long amount of time, you will set foot on solid, soft ground again. If the demons from the stairwell have stopped their yelling, you will not live to see the ground. If they have not, you will wish they had, for now is your opportunity to ask the only question to which the darkness will respond. You must ask firmly, "How can they be stopped?"
When you do, ghastly wails will emit from below you, though you will still be able to feel the ground under you. You will be able to sense the gentleman who led you here turn around. His eyes will pierce you, though you will not be able to see them. You must never look down or otherwise falter your gaze from the darkness immediately in front of you. The wails will continue, wordless at first, but a strong male voice will lead them into speaking in unison. They will tell you of the one thing that can prevent the result of the objects coming together, but it will be interlaced with every last consequence of doing so. They will tell you of the sky raining fire, of rivers running red with your blood, and they will tell you so much more.
When the consequences are finished, the lights will suddenly go on. The man who led you here will be gone. In his place will be an object that you will not be able to see in this place, lest it drive you completely insane. You must close your eyes as soon as the lights come on and feel around blindly on the floor for the warm, rough texture of the object. If you do not close your eyes, you will see what the ground is made of: disemboweled human corpses, all missing their eyes, though their mouths still breathe. If you look at this sight and are not driven mad immediately, you will become one of them, joining the satanic earth.
If you take the object successfully, though, you will be transported to the exterior of the asylum, where you may open your eyes.
The volcanic stone is Object 43 of 538. Though you know how to stop them from coming together, you will not be able to.