6mm. These are highly polished Black Line Agate gemstone beads. Each 16" strand of this Black Line Agate beads has a wonderful medley of brown, caramel, cream and black coloring. Agate gem stone beads enhance creativity and strengthen the intellect, making them a beneficial stone for both students and artists. Agate is also known as a good luck gem stone, and a stone of harmony. Agate beads balance yin/yang energy.