One of the greenest minerals you’ll find is malachite. It’s not yellow-green like olivine or blue-green like amazonite, it’s GREEN. When slightly acidic rainwater seeps into the ground, it can react with “primary” copper minerals there, sort of like how iron reacts with water to form rust. From that reaction, the water can pick up some of the copper, and if the water contains carbon dioxide, or if rocks in the area, such as limestone, contain carbonate minerals, a “secondary” carbonate copper mineral like beautiful green malachite can eventually form when the copper, carbon, and oxygen combine. It’s a little complicated! Malachite is considered a “secondary mineral” because it’s the result of a “primary mineral” (another copper mineral like chalcopyrite) breaking down into something else. That process can produce a bunch of different secondary copper minerals, but they’re almost always green or blue. Malachite can form in several different ways. It can look like a velvety coating, it can form balls like pectolite, it can create sharp-edged crystals that look suspiciously like azurite, hmm…, or it can form large swirly masses of all different shades of the same green color. The swirly masses, which these days almost all come from Africa, are often turned into stone carvings, especially of African animals, such as elephants. As for the suspiciously azurite-like crystals of malachite, those are called pseudomorphs, and they occur when you have an azurite crystal that turns entirely into malachite, but it still has an azurite crystal’s shape. (Morph means “form” in Greek.)