Abstract
We discovered two new metamict minerals in the Antsakoa I pegmatite near Berere in Madagascar. They were recrystallized through heating and investigated with the following results:
(1) Petscheckite, idealized as U4+Fe2+(Nb, Ta)2O8, hexagonal, space group P3lm, a = 6.42, c = 4.02A, Z = 1. It occurs as crystals up to 4 cm long and 2 cm thick, hardness ~5, specific gravity ~7. The color is black, streak brown-black, and fragments are opaque. Through oxidation and hydration, two intimately intergrown varieties occur: oxy-petscheckite, and hydroxy-petscheckite, .
(2) Liandratite, U6+(Nb, Ta)2O8, space group P3lm, a = 6.36, c = 4.01A, Z = 1. It occurs as crusts up to 2 mm thick surrounding petscheckite. The color is yellow to brown, streak bright yellow, hardness ~3 1/2, specific gravity ~6.8, refractive index n = 1.83 for metamict material. The structure of liandratite is identical with that of synthetic Ue+Ta2O8. The empty position at (0021) for this species is occupied by Fe in petscheckite.
The names are for Mr. Eckehard Petsch of Idar Oberstein and Professor George Liandrat of Samoëns, France, who have performed noteworthy prospecting activities in Madagascar. Both species were accepted by the IMA Commission on New Minerals and New Mineral Names.
