Some elements of Borderlands 3 will ask you to come back later to harvest them, long after you have unlocked Sanctuary 3. This is the case of the Eridian writings, as well as the many indestructible blocks of purple eridium crystals that you will encounter everywhere. Fortunately, the solution is actually simple, but it will take a little patience.
Destroy the purple Eridium crystals
To break these damn crystals, you simply have to move forward in history until you finish the ark of the planet Prometheus (about chapter 10). You will kill a rather memorable monster boss and enter a new ark, which will give you a new power to break the crystals with your melee attack (V by default on PC).
By destroying a block of crystals, you will obtain some erdium crystals (about 4). In addition, you can also release some of the chests blocked by these crystals, it will take two to three attacks and you will not collect erdium, but the contents of the chest are usually worth it.
Where to use the erdium?
You can spend your erdium crystals on board the Sanctuary, on the lower deck, near Crazy Earl's shop. A special vending machine that only accepts this currency will allow you to buy powerful weapons, cosmetics or other items.
Written by Robin "Raiden" Bouquet. Translated from French by Millenium.us.org