"Gravel-beam?" The husband of the witch Gróa. During the battle between Thor and the giant Hrungnir, a shattered fragment of whetstone became lodged in Thor's head. Gróa offered to remove the shard and sang her spells over him until the whetstone began to loosen.
When Thor thought that there was hope that the hone might be removed, he desired to reward Gróa for her witchcraft. He told her that he had waded from the north over Élivágar and borne her husband Aurvandil in a basket on his back out of Jötunheimr. One of Aurvandil's toes had stuck out of the basket and had been frozen solid; therefore Thor broke it off and cast it up into the heaves, where it became the star called Aurvandil's Toe. He added that it would not be long until Aurvandil returned home.
Gróa was so rejoiced at the prospect of her husband's return that she forgot her incantations; and so the whetstone was not loosened and remained in Thor's head.
- Skáldskaparmál, 17.