The spear of destiny (also referred to as "the Lance of Longinus", the traditional name of the centurion who officiated at the crucifixion) would have to have been one of a couple types: One, a standard "stabbing" spear (
hasta or
lancea). This would have been a fairly unremarkable looking thrusting weapon, the head shaped like an elongated leaf. It would have been socketed to the shaft. I'm not sure of the length of the shaft, but it wouldn't have been "pike length", probably more like 6-7 feet in length.
The second possibility would have been the
Pilum or military javelin. As the name indicates this is primarily a throwing weapon, and wouldn't make a very good thrusting weapon (at least not in a combat situation). The
Pilum was the primary arm of the regular legions.
For a description and discussion of the
Pilum , please check this link:
http://www.larp.com/legioxx/pilum.html
Since it is believed that the garrison at Jerusalem was staffed by
Auxilia (non-citizen recruits), it would be more likely that the spears used would have been of the "regular" thrusting variety (since that is what most authorities seem to believe the Auxiliaries used instead of the pilum), but this isn't necessarily so....
So the answer isn't clear as to which type of spear was used. However, I've seen at least one picture of one of the "spears of destiny" in some museum in Europe somewhere (sadly, I've forgotten where I've seen it), and if my memory of it is correct, it rather resembles a boar spear from the later middle ages....