It appears to be dirty. What are those imperfections?
Yes, inclusions, pits, and other flaws in the diamond which detract from it’s value. Black diamonds are slightly heavier and a tiny slight bit harder than other color diamonds. Only a very fractional percentage though. Heavier due to the inclusions and pollution that gives them the color. Harder is another question that I have not seen any research to explain why.
They also burn (yes, diamonds will burn) at a very slightly lower temperature than other diamonds… likely because of the inclusions and higher hydrogen content.