Veins and pipes are exciting geological features! They are sometimes visible at ground level by the soil surface, other times they are found at great depth. They vary in length, width and direction. In BetterGeo veins and pipes do not occur in oceanic crust under the sea (in reality they can but we have simplified things in this mod so you can only find them in the continental crust on land). They are formed when magma intrudes lateral and vertical fracture zones and other weak points in the host rock. This can happen near spreading zones between tectonic plates, rift systems etc.