Unlimited Gems 

is found in two forms: the black star diopside and the chrome diopside (which includes chromium, giving it a rich green color). At 5.5–6.5 on the Mohs scale, chrome diopside is relatively soft to scratch. Due to the deep green color of the gem, they are sometimes referred to as Siberian emeralds, though they are on a mineralogical level completely unrelated, emerald being a precious stone and diopside being a semi-precious stone.