The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs
"Rainbow Rock"- the detail with the perspective on the side facing away is a nice touch. If only the same care had been put into making the gradient more organic. plus a small, selective color palate is much more attractive than an easy rainbow.