《水经注·卷十四》
按注说：这种树木呈黑色，样子像炭，没有树叶；石头红色如朱砂，两块石头相磨擦，就能发出火花，把无灰的木头点着，可以终日燃烧不灭。
按注云：其木色黑似炭而无叶，有石赤色如丹，以二石相磨，则火发，以然无灰之木，可以终身，今则无之。
According to the notes: this kind of tree is black, looks like charcoal, and has no leaves; the stone is red like cinnabar, and when two stones are rubbed together, sparks can be produced, and the ash-free wood can be ignited and can burn all day long.