Black tourmaline bracelet with 20 beads that are 10 mm in diameter. Inside circumference is 19 cm.
 
Black tourmaline does not polish evenly and is not translucent (light does not go through it). Crystals in their natural form, have a growth pattern that presents with ridges or stripes like grooves on a record. Polished, it will show imperfections such as cracks, crevices and scratches that are visible under magnification. Black tourmaline has a nice sheen that is neither too shiny nor dull and it is heavier than black obsidian and back onyx.

Obsidian is not a crystal. It is glass formed by volcanic heat so presents smoother, with concentric curves, and shatters curvy like does glass. Obsidian has a very shiny, reflective surface, and is often transparent.

Black Onyx is jet black, may shows some lines, and is not transparent. Black onyx has a duller, not-so-polished finish and is heavier than black obsidian.