Labradorite

It is a very beautiful gem and is mainly produced in a fairly deep layer (Y axis 0 or less).
This gem is used to process as a decorative block or to make a new item "Amulet".
Equipped with "Amulet", it will notify you of the existence of enemy mobs.
It will be a countermeasure against the particularly scary Warden ...
If you have any other good ideas, let us know in the comments.
Thank you for taking a look at my thoughts.