Aegir's Fire

Why is gold called Ægir’s fire? The origin of it is this story:
Ægir, as was told before, went as a guest to Asgard, and when he
was about to return home, he invited Odin and all the Æsir to visit
him after an interval of three months. Undertaking this journey
were first of all Odin and Niord, Freyr, Tyr, Bragi, Vidar, Loki,
and then Asyniur, Frigg, Freyia, Gefiun, Skadi, Idunn, Sif. Thor
was not there; he was away in eastern parts killing trolls. And
when the gods had taken their places, Ægir had glowing gold
brought into the middle of the hall which illuminated and lit up
the hall like fire, and this was used as lights at his feast just as in
Val-hall there had been swords instead of fire. Then Loki wrangled
with all the gods there and killed a slave of Ægir’s called
Fimafeng. The name of another of his slaves is Eldir. Ran is the
name of Ægir’s wife, and the names of their nine daughters are as
was written above. At this feast everything served itself, both food
and ale and all the utensils that were needed for the feast. Then the
Æsir discovered that Ran had a net in which she caught everyone
that went to sea. So this is the story of the origin of gold being
called fire or light or brightness of Ægir, Ran or Ægir’s daughters,
and from such kennings the practice has now developed of calling
gold fire of the sea and of all terms for it, since Ægir and Ran’s
names are also terms for sea, and hence gold is now called fire of
lakes or rivers and of all river-names.


- Prose Edda, Skaldskaparnal