Tone

My sophomores are reading A Separate Peace these days, and I'd like to use the passage which appears below to teach diction and imagery as they relate to tone. However, I'm struggling with using the precise word to describe the tone. What do you think?

Passage:
Phineas had gotten up unnoticed from his chair. "I don't care," he interrupted in an even voice, so full of richness that it overrode all the others. "I don't care."
I tore myself from the bench toward him. "Phineas--!"
He shook his head sharply, closing his eyes, and then he turned to regard me with a handsome mask of a face. "I just don't care. Never mind," and he started across the marble floor toward the doors.
"Wait a minute!" cried Brinker. "We haven't heard everything yet. We haven't got all the facts!"
The words shocked Phineas into awareness. He whirled as though being attacked from behind. "You get the rest of the facts, Brinker!" he cried. "You get all your facts!" I had never seen Finny crying, "You collect every f---ing fact there is in the world!" He plunged out the doors.
The excellent exterior acoustics recorded his rushing steps and the quick rapping of his cane along the corridor and on the first steps of the marble stairway. Then these separate sounds collided into the general tumult of his body falling clumsily down the white marble stairs (176-177).