As a rare secondary mineral in the oxidized zone of bismuth- and arsenic-bearing mineral deposits.
Valid Species (Pre-IMA) 1832
In Germany, in Saxony, at the Neuhilfe, the Weisser Hirsch, and the Junge Kalbe mines, Neustadtel-Schneeberg; from Gadernheim, near Bensheim, Hesse; and the Neubulach and the Schmiedes
Link to MinDat.org Location Data.
Derivation not explicitly stated. Probably from the Greek for "incomplete," as the composition was undetermined when the mineral was first described.