The Mineral Storage is a 3x2 Resource room unlocked at level one. It increases the amount of Minerals the player's Starship can hold. It's recommended to have one onboard at all times, with two or three only onboard for large upgrades. After said upgrade, they should be removed.
The Mineral Storage visually changes based on the amount of Minerals its holding.
The second Mineral Storage was originally unlocked at level four and the third at level eight.