i have a large decorative bowl that i need to throw away. i was tapping it with my fingernails and almost managed to convince myself that it's plastic. i wasn't sure, though, so in order to test the material, i did what any sensible, responsible adult would do, and gave it a good tap with a hammer.
it's definitely glass.
(i didn't break the bowl but it made an impressive ringing noise. also it didn't even matter in the end because apparently non-packaging glass (that is, everything except jars and bottles) goes in the same bin as plastic where i am.)