The Collaborative International Dictionary of English v.0.48:

Peastone \Pea"stone`\, n. (Min.)
   Pisolite.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Pisolite \Pi"so*lite\, n. [Gr. ? a pea + -lite: cf. F.
   pisolithe.] (Min.)
   A variety of calcite, or calcium carbonate, consisting of
   aggregated globular concretions about the size of a pea; --
   called also peastone, peagrit.
   [1913 Webster]

   Note: Oolite is similar in structure, but the concretions are
         as small as the roe of a fish.
         [1913 Webster]