The small, hard, rock-like object in your foreskin is most likely a cyst, and probably benign as well. It does need to be checked, however, and Alice recommends that you see a urologist. If you are a Columbia student, make an appointment with Health Services by calling x4-2284, then pressing 2. If you are not a Columbia student, call your pediatrician for the name of a urologist. It is great that you noticed this, and have the impetus to learn more about your body.
Some people let their fear or discomfort interfere with their getting good health care.