Originally this resource could only be found underground on most planets, however it is now only found very deep underground on Sylva or on mountaintops, or underground on Calidor, making it much more rare than originally.
In the real world, malachite is just one of many copper ores, though it is considered to be one of the prettier ones. This term in its etymology comes from France under the name "malachite" and with it from the Greek "μαλαχη" (malachē) which means mauve because of its greenish color.