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.)
In the canon of scripture the answer is not stated, but in the book of Jasher it is. I suppose most would not consider it doctrine since it is not in the current Bible, but in the book of Jasher it states:


  And Cain hastened and rose up, and took the iron part of his ploughing instrument, with which he suddenly smote his brother and he slew him, and Cain spilt the blood of his brother Abel upon the earth, and the blood of Abel streamed upon the earth before the flock. (Jasher 1:25)


This is the only reference I have found that may actually mean something besides just guessing at it.