Gungnir Properties

Why is gold called Sif’s hair? Loki Laufeyiarson had done this
for love of mischief: he had cut off all Sif’s hair. And when Thor
found out, he caught Loki and was going to break every one of his
bones until he swore that he would get black-elves to make Sif a
head of hair out of gold that would grow like any other hair. After
this Loki went to some dwarfs called Ivaldi’s sons, and they made
the head of hair and Skidbladnir and the spear belonging to Odin
called Gungnir. Then Loki wagered his head with a dwarf called
Brokk on whether his brother Eitri would succeed in making three
precious things as good as these were.

[...]

And then the smith came back, saying it had come close to everything
in the forge being ruined. Then he took from the forge a hammer,
then handed over all the precious things to his brother Brokk and
told him to take them to Asgard and fulfil the wager. And when he
and Loki produced the precious things, the Æsir took their places
on their judgment seats and the decision uttered by Odin, Thor,
Freyr was to be final. Then Loki gave the spear Gungnir to Odin,
the head of hair which was to be Sif’s to Thor, and Skidbladnir to
Freyr, and announced the features of all the precious things, that
the spear never stopped in its thrust, the hair was rooted in the
flesh as soon as it came on to Sif’s head, and Skidbladnir had a fair
wind as soon as its sail was hoisted, wherever it was intended to
go, and could be folded up like a cloth and put in one’s pocket if
desired.


- Prose Edda, Skaldskaparmal