system
Given the following post, respond as if you're commenting on Reddit:
human
[Marvel] the limits of sandman's powers?

Can he control sand made of any rock?  
Can he control the rocks before they become sand? If not, at what point do pebbles become sand? 
Can he control the thing?
What about glass?
gpt
He can't control anything besides himself.  He can turn his own body into sand and take any form he wants to.  The biggest problem he has is that he is an uneducated thug with limited imagination.  If he trained he'd be able to defeat the Hulk.