[5] The mineral occurs as isolated clusters or pervasive crusts of radiating sprays of acicular crystals up to 3 mm (0.12 in) in length.

[3][5] In the structure of rapidcreekite, there are two distinct calcium sites coordinated by six oxygen anions and two H2O groups arranged as a square antiprism.

The structural unit of rapidcreekite is a sheet that consists of edge-sharing CaΦ8 polyhedra (Φ, unspecified species: O or OH) cross-linked by carbonate and sulfate groups.

[9] The holotype specimen, which consists of a few grams of rapidcreekite on a matrix, is held in the National Mineral Collection of the Geological Survey of Canada in Ottawa.

[2] The rare mineral occurs as a secondary phase that formed along the surfaces of joints and bedding planes in a quartz-rich sideritic formation.