I'm sure this is old news here, but here's a piece on prison rape with some interesting stats.
Here's a quote with some of the highlights:
13% involved white inmates raping white inmates
29% involved black inmates raping black inmates.
56% involved black inmates raping white inmates.
This comes to a grand total of 85% of prison rapes being committed by blacks, with 69% of the victims being white. The rapes of white inmates are normally done by gangs of blacks and somewhat in the open so that other inmates, but not staff, can witness the attacks.