Black Onyx round semi-precious stone beads. These 4mm gemstone beads are black in colour and believed to promote steadfastness and determination. Black Onyx is a banded stone that is commonly coated with a shiny black layer for jewellery use, as is the case with these beads. These gemstone beads are sold either singularly or strung on a 16 inch/40cm strand of monofilament which contains approximately 100 4mm beads. They are a very versatile size and ideal for bracelets and tiaras.