Was formed about 2.6 million years ago. The Great Dyke is a 310 mile rock formation that stretches across the center of Zimbabwe. More than 250 color combinations of the stone have been identified. A hardness level for the stone varies from 1.5 to 6.5. Referenced as Serpentine because of the serpent like bands of green color. Common colors are olive green, black and reddish-brown.