The Collaborative International Dictionary of English v.0.48:

Eaglestone \Ea"gle*stone\, n. (Min.)
   A concretionary nodule of clay ironstone, of the size of a
   walnut or larger, so called by the ancients, who believed
   that the eagle transported these stones to her nest to
   facilitate the laying of her eggs; a["e]tites.
   [1913 Webster]