Phostlite (fr: calystène) is a metallic element discovered in a large meteoroid which passed close to planet Earth in the mid-20th century. It was named after its discoverer, Belgian astronomer Prof. Decimus Phostle, who also took part in the expedition to retrieve a fragment of the meteoroid which fell in the Arctic Ocean, where it remained afloat as a small island. The island began to sink, but fortunately a small piece of Phoslite was recovered by the reporter Tintin.
As it turns out, exposure to Phostlite has the curious effect to accelerate the growth of living organisms, including mushrooms, apple cores, maggots, and spiders. These creatures, when in the presence of phostlite, have been observed to grow to gigantic sizes and rapidly mature. Conversely, it doesn't seem to have any effect on intelligent beings, as both Tintin and Snowy remained unaffected. Mushrooms seem to spontaneously grow out of Phostlite and explode once they have gotten big enough. In addition to causing growth, Phostlite also causes maturity, as seen when it turned an apple core into a massive apple tree and a maggot into a tremendous butterfly.