Alicia Keys

I was listening to Alicia Keys’ Empire State of Mind and heard the phrase “On the corner selling rock, preachers pray to God”. What does she mean with “corner selling rock”?
Thank you

uhh… I think it means “…on the street selling crystal meth”
…I think.

On the street, selling crack-cocaine.
Crack-Cocaine, also known as just crack, is a freebase version of cocaine that you can smoke. Very cheap drug sold to poorer people, mainly poor urban people, largely black/African American.

Thank you very much both of you!