The Witch and the Lich; Rolling Stone

Credits; Rea, Krell,

Krell stooped and gathered some of the bloodstone powder into a vial.  It would come in handy later; of that he was certain.  If nothing else, it would make a decent lamp. 
Rea was waiting at the door.  She was trying to secret her admiration of his handiwork.  She had her pride, and apparently she wasn't comfortable with the idea of his knowing things she didn't.  He didn't blame her, it was probably embarassing to have someone so much younger manage a spell of which she had no prior knowledge. 
"So, on to the next room then?"
Krell nodded.  He shielded the door once more and after Rea had made sure the room was safe they both enter.  It was dark, so he clasped his hands and prepared to produce a small light to follow them.  Before he could cast the spell though, Rea stopped him. 
"It's dark, let's just keep it that way."
"You think light might activate a trap then?"
"No, I just like the dark."  He could tell she was smiling, even through the darkness.  She was also making fun of him, possibly to reassue herself of her own greater prowess in adventuring. 
Krell felt at the walls, and noticed that the hall was both narrow and circular.  He remembered the door being round as well and had a sudden realization. 
"This room is a tube."
He heard Rea shuffle about.  She was shorter, as were her arms, and it took her more effort to feel out the room.  after several minutes of shuffling he heard a clicking noise.  A rumbling began and Rea cryed out, "Y'know what, go ahead and turn the light on.  I don't think it matters now."
He quickly conjured a small orb of light to follow him and the darkness, magical as it likely was, retreated before it.  It took only a second to find the source of the rumbling.  A large, perfectly spherical boulder was rolling right at them down the tube. 
"Run!"
Krell turn and began to escape as fast as he could.  He felt a hand on his robe before he could get further than a foot and stopped. 
"Stand still, I need that light and it keeps darting around when you move."  Rea jumped up and took hold of the little orb of light he'd conjured.  She stepped forward and pitched into the stone's core.  Krell saw her intent and added strength to the light.  Rea flipped the blades from her gauntlet and aimed directly at the stone.  A light grew between them, and shot into the stone.  It shattered into dust while still moving, causing a wave of stone fragments to fly past them. 
"did you increase the strength?"
"Yes."
"Did you doubt I could handle it?"
"No, I just thought it would help."
"Well it did.  Thank you." She continued towards the next door, tapping the light that lingered at what had once been the stone's core and it followed them further into the vault.