Oreberry bushes are bushes commonly found in caves that will cause the same effects of a cactus if touched (Ex, standing on, walking into etc, but it does much less damage and will not destroy items, but most importantly grow "berries" of metal, such as aluminum and tin. the most common (aprox.) is aluminum. The berries will regrow but it is important that it is in a dark room otherwise the bush will sit there and do nothing.
Now i know what you're thinking "it is free aluminum, tin and copper!!!" but each berry can only give 1/9 of an ingot, or if smelted in an oven will create a nugget. But a significantly large farm could possibly produce many ingots an hour, however could not be automated (as of now).