They can - if fired from a powerful slingshot.
Marbles are often used as alternative slingshot ammo. In this regard, The Slingshot Channel tests two very common myths:
- Can marbles penetrate flesh?
- Will marbles shatter when they hit a hard surface?
These myths are checked out, using ballistic gelatin and a solid wall. See the harmless looking glass balls tearing the gelatin into shreds, and see how they chip stone shards from a massive rock...
The message is clear: Marbles are about as dangerous as steel balls when fired from a powerful slingshot.