[quote=@KoL]
[@Zaphander]

The description of your character's quirk is a little bit vague when it comes to his resistance to damage while transformed, just to make it clearer, how much could he fall before getting any serious damage from say... hitting a concrete sidewalk? As in how high of a building could he jump from without fearing that he would break himself on impact?

Also, since he doesn't breathe while transformed, how long can he remain in that form without suffering choking himself?

Lastly, I suppose that he can only use his phone to alert heroes that he knows the number of, right? Unless he has another way of getting people's phone numbers, without them giving it to him, of course.
[/quote]

I would say a ten stories tall, so around 100 feet or so, would be the safest average height before he would take notable damage from falling onto solid concrete. 300 feet would be about as lethal as anyone else falling without some sort of quirk that could negate the damage. Of course if he falls on something like say, a sharp pipe or a jagged piece of rock, that's even more risky since all that weight concentrated to that point could shatter and possibly impale him. 

Also he doesn't need to breath in rock form, but that doesn't mean he has to either. He could stay in his rock form indefinitely until enough damage occurs where he would shatter or he chooses to get out when he's not moving. Shattering in this instance would be if he looses at least 10% of his mass in whatever form he's in, with smaller forms being easier to shatter than bigger ones thanks to how relatively small 10% would be. This way he could so something like say, turn into a small rock and hide in a forest or under some water. Though he still can feel tired, hungry, sick, etc, but these are usually only because he was already suffering from one of those things before he transformed.

As for his phone I figured there was a sort of hero hotline for when you need immediate attention, and not just police level assistance. Like if 911 calls for the police, maybe there's another number that calls for heroes. It's why it's used only for dire emergencies like if there's a legit villain on the lose blowing things up and burning buildings down and not just a random purse snatcher. I guess I could say the number would alert a specific hero agency if Peter knows their number.