Detailed studies (i.e., Boles et al., 1985; Thyne and Boles, 1989; Scotchman, 1991; Mozley and Burns, 1993; McBride et al., 2003; Chan et al., 2005; Mozley and Davis, 2005) published in peer-reviewed journals have demonstrated that concretions form after sediments are buried but before the sediment is fully lithified during diagenesis. They typically form when a mineral precipitates and cements sediment around a nucleus, which is often organic, such as a leaf, tooth, piece of shell or fossil. For this reason, fossil collectors commonly break open concretions in their search for fossil animal and plant specimens.