I thought they were iron, but someone told me they were actually bronze. I did a bunch of searching and everywhere I look seems to say they were a different material, though most of them say they were iron.
Does anyone know a reliable source that would let us know for certain?
Edit: To be more specific, by 'weapons' I mean their spearheads, and their shortswords.
To answer this one must consider both the rank and status of these soldiers and also the time period.
300BC is generally considered as being within the Iron Age, where Iron, instead of Bronze, was being more widely used. This began at an estimated time of 800BC, a good 500 years before Thermopylae.
Further, if one considered that these 300 Spartans (please do bear in mind that there were at least 6000 other soldiers from all over Greece fighting in the same battle) were Hoplites who were the among the heaviest armoured Spartan Infantry we can assume that they had the best equipment.
Further, they fought with their King, who one would assume to have the best armour and weaponry money could buy and have his best men with him.
Thus, if we consider all such factors we would conclude that generally the Hoplites would have iron short swords and iron blades on their spears. Bronze was mainly used in their armour (breastplate and, in particular, greaves. However, their breastplate tended to be rather heavy and so more commonly used were bits of hardened fabric glued together).
It would be somewhat understandable that people you've talked to would assume they had bronze weaponry as bronze was still a good metal to use as a weapon and they did have bronze armour, but the problem with bronze is that it bends very, very easily and if we consider that these soldiers fought for several days and for several hours on each of these days it wouldn't be very likely that they would have bronze weaponry as it would bend and break during the conflict.
Hope I answered your question.