41. The second feature contained seven concretions . 42. Many Pierre Shale ammonites, and indeed many ammonites throughout earth history, are found inside concretions . 43. In concentric growth, the concretion grows as successive layers of mineral precipitate around a central core. 44. Concretions are often exposed at the surface by subsequent erosion that removes the weaker, uncemented material.45. After further study it was decided that the blueberries were concretions formed in the ground by water. 46. These concretions occur as both spherical cannonball concretions and flat, disk-shaped or oval concretions. 47. These concretions occur as both spherical cannonball concretions and flat, disk-shaped or oval concretions. 48. These concretions occur as both spherical cannonball concretions and flat, disk-shaped or oval concretions . 49. The iron oxide concretions found in the Navajo Sandstone exhibit a wide variety of sizes and shapes. 50. It forms massive to reniform pappillary aggregates in fractures, bottryoidal concretions in laterite or fracture infill.
