Onyx bracelet

Exploration Stage: Hall of Weddings
From: Martha
Description: You chose an unusual accessory. Look at the bracelet the woman in the black dress is wearing on her hand. It's black onyx. It is a magical gemstone used in many black magic rituals. Even I don't wear it casually. Where can I find it?
Completed: Look at this. The stones in this bracelet are jet black! It's as if they are avoiding even light. The surface is not even reflective! Inside there is the letter M. It's the same letter that was on the sorcerer's signature.