Sardonyx is a variety of microcrystalline quartz chalcedony (kal-SED-oh-nee), also known as Black Line Agate, is a dramatic black stone banded with crisp white lines, translucent bands and the occasional venture into the brown and cream and is found all over the world. It's a stone of strength and protections. Mohs hardness 7.
Metaphysically - it is believed to improved memory and increase your analytical talents.
We do our best to choose consistent stock, but the nature of natural stones is that there will be some inconsistency between strands and between individual beads.