A crystal tear formed slowly over the ages where the Erdtree's bounty falls to the ground.
Can be mixed in the Flask of Wondrous Physick.
The resulting concoction prevents one's runes from being lost upon death. However, the effect lasts only for a short time.
Prevents the loss of Runes upon death for 180 seconds (except for deaths caused by Death Blight).
Notes
Like the Sacrificial Twigs, since it prevents you from dropping a Bloodstain with your runes upon death it will also prevent it from replacing your previous one and therefore gives you another chance to grab it.
This is especially useful around large drops since it makes the consequences around fall damage deaths much smaller.
Keep in mind the time limit, as while 3 minutes is a fair amount of time it's still a limited amount of time and it may run out at the worst of times in an area.
Usually best saved for a run through or fight against dangerous enemies, or just before starting a section with falls.
Can be used to transport out a bunch of Runes stuck inside of a boss room, especially when combined with quitting out to the main menu to reset the character to just outside of the boss room's fog wall.
See also
Sacrificial Twig, a type of talisman with the same effect that breaks upon death.