Malachite

Malachite is hard to mistake for anything else: vivid green, with rings and bands that look like a cross-section of a tree trunk, or a topographic map of hills. The color comes from copper, and the rings form as the mineral is deposited in layers, one on top of the other, in cracks and cavities in the rock.

The name comes from the Greek malache, mallow, because its color reminded people of the plant's leaves.

Malachite is also a copper ore, and people have been mining it for thousands of years. According to Wikipedia, it was mined and smelted for copper in the Timna Valley more than 3,000 years ago, and according to Hebrew Wikipedia it can still be found there today. The ancient Egyptians ground it into a green powder for makeup, and until about 1800 it was used as a green paint pigment.

The Russian tsars were especially fond of it. Large quantities were mined in the Ural Mountains, and it decorated their palaces. The Hermitage Museum has an entire hall called the Malachite Room. And for those who prefer sport to palaces: according to Wikipedia, the base of the FIFA World Cup trophy has two layers of malachite.

Now for the warning: malachite is soft, 3.5 to 4 on the Mohs scale, and has perfect cleavage. According to Geology.com, it is also sensitive to heat and reacts with weak acids. In other words, it does not like knocks, it does not like heat, and it does not like lemon juice either. That same softness makes it easy to grind into powder, which is what made it such a sought-after pigment.