This item, with an interesting appearance for several decorations, is already used by many people, this tutorial is not aimed at them. The purpose of this short article is to teach you how to get out of the crystal cave (from Thaian's mission of the Feaster of Souls Quest) and not lose the crystals, as is normally the case.
To do this is very simple, follow these steps:
Collect the desired amount of crystals inside the cave.
Exit the stairs, but don't walk, stay still.
Place your luminescent crystals in a backpack, to facilitate in case of more than 100 crystals. [optional].
Throw your backpack, or loose crystals (if you prefer) away, at the ends [Extremes] of the screen of preference.
Go freely to the south, an effect (which usually makes the crystals disappear) will appear.
Collect your backpack / crystals again.
Use your crystals at will.
A quick video below, for example.