How did Cain kill Abel?

Genesis 4:8 > Cain said to his brother Abel, “Let us go out in the field.”* When they were in the field, Cain attacked his brother Abel and killed him. \* [4:8] Let us go out in the field: to avoid detection. The verse presumes a sizeable population which Genesis does not otherwise explain. My question is *how* did Cain kill Abel? I was wondering if there is a commonly accepted method of murder, or if a religion, such as Catholicism, has a tradition about how he was killed. I have read that he used a rock. I think the more believable guess is a spear. (Based off of the meaning of the name Cain.)