Whiterockite, CaMgMn3+3O2(PO4)2CO3F·5H2O, is a new phosphate–carbonate mineral from the White Rock No. 2 quarry, Bimbowrie Conservation Park, South Australia, Australia. The mineral is associated with dufrénite/natrodufrénite, ushkovite, bermanite, leucophosphite and sellaite in a matrix comprising fluorapatite and minor quartz. Whiterockite has formed from hydrothermal alteration and weathering in an oxidising, low-temperature and low-pH environment. Whiterockite forms aggregates of thin platy dark-red crystals up to 0.7 mm across with individual crystals up to 0.2 mm in across. Crystals are transparent with a vitreous lustre. The mineral is brittle, has a perfect cleavage on {001} and has an irregular fracture. The measured density is 2.76(2) g/cm–3. Whiterockite is optically biaxial (–), with α = 1.660(3), β = 1.760(5) and γ = 1.770(5), determined in white light; 2Vmeas = 30(1)°; and orientation: X ≈ c*. The mineral is pleochroic: shades of red brown; X < Y < Z. Electron microprobe analyses provided the empirical formula (Ca0.87Na0.18)Σ1.05Mg1.05(Mn3+2.87Fe3+0.10)Σ2.97O1.93(PO4)2.01CO3F1.04·4.99H2O. Whiterockite is monoclinic, C2/m, a = 11.112(2), b = 6.4551(13), c = 10.667(2) Å, β = 102.61(3)º, V = 746.7(3)Å3 and Z = 2. The crystal structure of whiterockite has been refined using single-crystal synchrotron X-ray diffraction data to R1 = 5.10% on the basis of 957 reflections with F0 > 4σ(F0). The structure can be described as a layered structure formed by the stacking along [001] of three kinds of layers and is related to the structure of jörgkellerite.