Hand strung 16" necklace with a 2" extension. The Black Onyx round beads measure approximately 6mm in size and are spaced round and textured silver beads. It's the right size to wear everyday or put your favorite pendant on it to make it a little more personal. Onyx is a chalcedony quartz that is mined in Brazil, India, California, and Uruguay. It has a fine texture and black color; however, some onyx also displays white bands or ribbons against a black or brown background and this variety is known as sardonyx. The name comes from the Greek word onyx.