The formations known as the Brainlands are formed by the slow up-thrusting of material from beneath the planetary crust through narrow vents. As the semi-molten rock is extruded it creates a creased bifurcate formation which looks not dissimilar to a human brain on a thick stalk.
The individual formations continue to grow over millennia, and range in size from midgets only ten or twelve metres in diameter to giant formations over 200 metres tall, and perhaps 300 metres in diameter. As the individual "brains" grow, they crowd up against each other and their crowns merge like the flowerlets of a cauliflower, creating a labyrinth between their stalks below.
The Brainlands are known primarily as the source of the rare earth Plauttite, widely used in the Terran cosmetics industry, but the upwelling rock carries with it a number of other elements which are also mined.
The level of background radiation in the tunnels beneath the brain-crowns is considerably higher than that normally considered healthy, but it is well within safe limits as long as certain elementary precautions are taken before venturing in.