A tough, silicified limestone formerly used to make millstones.It is typified by the presence of multiple cavities that originally housed fossilized shells.

 
  • 磨石,砂质多孔石灰岩一种坚硬的,硅化石灰石,以前用来制作磨石。具有最初由化石化的贝壳而形成的多孔特征
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