Studies of uranium minerals (XVI): an alteration product of ianthinite¹

A specimen from Katanga labeled ianthinite and consisting of purple-colored minute needles and laths was sent by J. F. Vaes to the Harvard University mineral collection several years ago. The mineral resembles ianthinite in the hand specimen, but chemical analysis gave only a trace of UO₂ and a formula of UO₃ · 2H₂O (Table 1), although ianthinite reportedly contains only quadrivalent uranium and has a formula of 2UO₂ · 7H₂O (Schoep, 1930). The mineral probably is an alteration product of ianthinite in which the U⁴ is almost completely oxidized to U⁶; it may be epiianthinite, inadequately described by Schoep and Stradiot (1947). The purple color of the mineral is due to the trace of UO₂. Although epiianthinite is yellow, the optical properties of the alteration product are more like those of epiianthinite than those of ianthinite (Table 2).