It is recommended that players deposit Diamonds of Azzanadra in the bank as soon as they obtain them, as a level 116 stranger may appear and attack anyone holding one of these gems. Each additional diamond in one's inventory increases the likelihood of being attacked.
This diamond was formerly known as the "shadow diamond", then was changed to the "rock diamond", and then back to its current name.
If, for some reason, you would like a duplicate of this diamond, you can get one. Equip your ring of visibility, before dropping the first diamond. Enter the caves and run to Damis' chamber (bathing in the salt-water spring is recommended). Pick up the diamond, and run back. If you do this quick enough, you can pick up the first diamond before it disappears. It may take a couple tries to get correct.