Another example of plain old quartz that becomes valuable if you just add a little something, chrysoprase is a gemstone created when a small amount of nickel combines with quartz, producing a lovely milky green color. Specifically, like agate and others, chrysoprase is a type of chalcedony, which is a type of quartz. So what type of quartz is chalcedony? It’s “cryptocrystalline” quartz. When you look at a cryptocrystalline mineral like chrysoprase, you just see a smooth surface, not sharp-edged crystals. Chrysoprase usually forms by filling in cracks in rock, and it’s often found in a serpentine-related rock called serpentinite. If you find raw chrysoprase chunks in nature or at a mineral store or show, they’ll often have thin layers of rusty-colored rock on the bottom and top that contrasts with the green chrysoprase, and the color of those thin layers can be from iron in the surrounding serpentinite.