Onyx beads can be any of a wide variety of colours, but black is very common. Onyx is a banded variety of chalcedony, made of bands of chalcedony in alternating colours. Onyx has a long history in jewellery because it is rich looking yet affordable.
Our Semi Precious Stones are genuine and natural unless they are stated to be synthetic in the description. However, you will find the vast majority of Semi Precious Stones are treated in some way, as they would not be stable enough for use in jewellery in their original state.