Face-sharing trimers in the structure share octahedron corners, forming chains of octahedra extending in the direction of the b-axis.
Adjacent chains formed from two trimers and (PO4) groups extending along the direction of the a-axis, resulting in sheets parallel to (001).
More rarely, rockbridgeite can also form in sedimentary rocks in association with limonite from iron ore deposits.
Other localities for rockbridgeite include sites in Brazil, Portugal, Bavaria, Saxony, South Australia, Namibia, Zimbabwe, and Morocco.
Type material is conserved for reference in Harvard University in Cambridge, Massachusetts, United States.