This is a particularly nice cabachon of Chinese Writing Stone (basalt porphyrite), which is a dark green stone with whiteish inclusions that look like the Chinese written language.  It is often found in the area around Auburn, CA.  I have bezeled this cabachon with dark green, gold and very light green/white beads, which are also used in the rope. The necklace measures 20" long and is finished with a beaded toggle clasp.