What is Aegir Gold used for?

In God Of War, Aegir Gold is basically most common resource - you can get a plenty just by roaming around Lake Of Nine. After finishing the game, I had around 1000 of this resource. Yet, I haven't found a single application to it, except selling it. Judging by the amount of Aegir Gold game gives you, it could be basic crafting material needed for everything, but I haven't found literally a single item requiring this resource to craft.

So, my question is - what's the purpose of Aegir Gold?

PS: I consider the possibility of this to be a persistent source of Hacksilver, yet it is really weird decision to give a player resource to sell instead of actual currency.

According to this materials guide, Aegir's Gold is:

Used to upgrade armour and buy Runic Attacks.

This guide describes also all possible materials locations and uses, tradeables and special materials.

This post on PlayStation Universe goes the same way:

You can then use it to upgrade gear.