Black Star Diopside for sale at wholesale prices. Black Star Diopside is rated at 5.5 on Moh‘s Scale of Hardness and though it is suitable for jewelry purposes, care should be taken with this stone for it is relatively soft and brittle. This opaque stone is generally black in color but can occasionally be found with shades of green. Black Star Diopside exhibits a star like phenomenon known as Asterism. These stones contain inclusions in the form of needles that align to produce the white 4-rayed star. It is unique because it is the only gemstone to exhibit a 4-rayed star.