Arsentsumebite forms good, colorful specimens and is a popular collection mineral, although quite rare. It is closely related to its cousin, tsumebite. The two minerals are in a series in which the arsenate ion group in arsentsumebite is replaced by a phosphate ion group in tsumebite. The two differ only slightly; this is mostly because the structure is the same in the two minerals. Both are formed in the oxidation zone of lead-copper ore deposits.
Both minerals are unusual in that they have two ion groups instead of the usual one in most minerals. It the case of arsentsumebite, it has an arsenate ion group and a sulfate ion group. Mineralogists prefer to classify it as a phosphate (where arsenates are placed) because the arsenate ion group has a higher negative charge (-3) than the sulfate group (-2).