old joke I heard in primary school...

Once upon a time, there lived a princess, in a place far far far away.
This princess was special. She was the most beautiful princess in all the fairy tales ever told.
Unsurprisingly, there was also a witch. A most hideous witch, who despite all her powers would forever be ugly and remain bitterly jealous of the beautiful princess.
One day, when her jealousy overtook her, the witch kidnapped the princess and locked in a high tower.
Upon finding out that her daughter had been kidnapped, the king sent out a decree to the land, saying that whosoever rescues his daughter can have her hand in marraige.
A prince, obviously good looking and riding a white mare (whoops, don't forget the shining armour), volunteers. He bravely rides to the tower of death. He kicks down the front door, races up the steps on his valiant steed and bursts into the top chamber, with the splinters of the broken door preceding him. He raises his super powerful sword which was forged on the highest mountain in the darkest cave from some fallen meteor rock and poises to strike down the witch, but the witch grins, lifts her wand and casts a spell. The prince's super powerful sword melts and looks in disbelief as the witch turns him into a toad.
Another prince, obviously at least as good looking as the first and with the same white mare volunteers to go next. He replicates the actions of the first prince, and upon the witch, he raised his super powerful sword, crafted in the deepest ocean by the smartest crab from the very elements that formed the core of the earth. The witch blushed, because the prince was so good looking. Then, she lifted her wand, cast a spell, melted the super powerful sword and turned him into a toad.
The two toads hoped off together, in search of a princess willing to kiss them...
In the meantime, a third prince, not as good looking (almost ordinary in fact), riding a donkey, decides to rescue the princess. He opens the door to the tower. Labouringly, he trudges up the steps, and panting, he stumbles into the room where the witch stood waiting and the princess sat in fear. The prince unsheathed his very mysterious and very dark sword. The witch, having done this twice already, felt confident as she raised her wand and started her incantations. The sword did not melt! With a swift stroke, the prince parted the air and the witch's head from her neck. The princess was rescued and the prince was locked up in marraige forever and ever...

What kind of sword was the third prince wielding?