The cations Na, K, NH4, Ca, Mg, Mn, and, in certain instances, Ba, Sr, and Pb combine with the anion SO4 to form 58 mineral species. Slightly more than half are hydrous, and several contain Cl, F, or CO3. Infrared absorption spectra of most of the above sulfate s have been obtained with a split beam infrared spectrophotometer. The identity of each species examined has been verified optically and by means of X-ray diffraction for further confirmation. Where infrared curves have been previously published, the absorption bands obtained have been compared with data in the literature.

Examination of the spectra indicates that the sulfates yield infrared curves that fall naturally into several groups. These groups are outlined, and the relative ranges in absorption characteristics are given for each.

Structural analysis is beyond the scope of this paper, but attention is directed toward such structural features as may be compared with those of previous structural studies.

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