Physiologus [ca. 4th century CE]: Piroboli rocks exist only in the East; they are igneous rocks of masculine and feminine gender. As long as they are separate from one another, they do not burn, but, if the male approaches the female, fire breaks forth and consumes all. - [Curley translation]

Aberdeen Bestiary [circa 1200 CE] (folio 94r): On a certain mountain in the east, there are fire-bearing stones which are called in Greek terrobolem; they are male and female. When they are far from each other, the fire within them does not ignite. But when by chance the female draws near to the male, the fire is at once kindled, with the result that everything around the mountain burns.

Guillaume le Clerc [ca. 1210 CE] (Bestiaire, Chapter 3): In the East there far above / Are two stones on a high mountain / Which have a very strange nature, / For they bear fire and heat, / They are as male and female. / Did you ever hear a story / More wonderful or more true, / For the books make us believe it? / When these stones are far apart, / Fire does not issue for any purpose / But when by chance it happens, / That the one comes near the other, / They kindle and fire comes out / Which burns up both the stones, / And so greatly the fire waxes and grows / That it kindles all the mountain / And whatever there is on each side / Of the mountain kindles and burns. - [Druce translation]