Obsidian. Obsidian bracelets are relatively cheap. Most customers buy expensive jewelry, so the gold shop will give away such bracelets.
Your black is stone or agate. The price of the gold shop is not too high.
Landlord, I'll show you two kinds of crystal diagrams close to what you said.
Under normal circumstances, the obsidian in the gold shop is relatively secure and its authenticity is relatively large. Obsidian (English name: Obsidian) is a common black gem and volcanic crystal, also known as "Dragon Crystal" and "Ten Victory Stone". It is a naturally occurring silica, usually black.
The black bead bracelet you mentioned should be obsidian bracelet. It depends on how many beads you use and whether you match them with gold beads. If you don't deserve the golden ball, a bracelet is about five or six hundred yuan.