What sort of weapon is Jack using to hunt pigs in Lord of the Flies?

Jack uses a spear to stick the pig and a knife to cut its throat. 

The pig-hunting is very important to Jack and to the other boys on the island.  It is about much more than getting meat.  Jack also just wants to kill something, because he has an innately savage nature.  He was also appointed head of the hunters, so he considers it a failure if he doesn’t get a pig. 

Killing a pig turns out to be more difficult, physically and psychologically, than the boys ever imagined.  The first time there is a pig, Jack finds himself unable to stick it.  It would be the first time he killed something.  The enormity of it overwhelms him.

He raised his arm in the air. There came a pause, a hiatus, the pig continued to scream and the creepers to jerk, and the blade continued to flash at the end of a bony arm. (Ch. 1) 

The boys continue their desperate efforts to kill the pig.  They even develop a song and dance centered around pig killing.  It is symbolic of their new life and existence on the island.  They want to be self-sufficient and grown-up.  Jack uses a “sharpened stick about five feet long” to hunt the pig. 

From the pigrun came the quick, hard patter of hoofs, a castanet sound, seductive, maddening—the promise of meat. He rushed out of the undergrowth and snatched up his spear. The pattering of pig’s trotters died away in the distance. (Ch. 3) 

The pig dance became more disturbing when they had a boy actually playing the pig.  Robert screamed and struggled while “Jack had him by the hair and was brandishing his knife” (Ch. 7).  One boy had already died in the fire, and soon Simon and Piggy would also lose their lives to the boys’ frenzied and desperate worship of hunting.