more

Quirrell, however, must have been braver than they'd thought. In the weeks that followed he did seem to be getting paler and thinner, but it didn't look as though he'd cracked yet.
Every time they passed the third-floor corridor, Harry, Ron, and Hermione would press their ears to the door to check that Fluffy was still growling inside. Snape was sweeping about in his usual bad temper, which surely meant that the Stone was still safe. Whenever Harry passed Quirrell these days he gave him an encouraging sort of smile, and Ron had started telling people off for laughing at Quirrell's stutter.
Hermione, however, had more on her mind than the Sorcerer's Stone. She had started drawing up study schedules and colorcoding all her notes. Harry and Ron wouldn't have minded, but she kept nagging them to do the same.

What’s the part of speech of ‘more’ in the example, and what’s the meaning of it?