The following data have been obtained by the Weissenberg and powder diffraction methods:

Holdenite. Unit cell dimensions: a0=11.97kX, b0=31.15, c0=8.58. Space group Bmam. Cell contents 2[(Mn,Ca)25(Zn, Mg, Fe)15(AsO4)7(OH)33O13]. Specific gravity 4.118 (calc.), 4.11 (meas.).

Mooreite. Unit cell dimensions: a0= 11.18 kX, b0 = 20.25, c0= 19.52. Space group P2i/m. Cell contents 13[(Mg, Mn, Zn)8(S04)4H2O]. Specific gravity 2.543 (calc.), 2.47 (meas.).

Delta-mooreite, originally thought to be a chemical variant of mooreite, is a distinct species. The new name torreyite is proposed for the mineral.

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