Aetherium

This is a precious resource that can be mined from one of the main structures you’ll be building—or digging, rather. It’s essentially raw aether that is processed out of deposits from the stone in your guild hall. These deposits are extremely rare in Tyria, making your guild hall a very valuable find! Aetherium will be generated automatically over time by miners working in your guild’s mine. You’ll be able to upgrade the rate at which the aetherium is generated as well as your capacity to store it. https://www.guildwars2.com/en/news/building-your-guild-hall/