Redcanyonite, (NH4)2Mn[(UO2)4O4(SO4)2](H2O)4, a new zippeite-group mineral from the Blue Lizard mine, San Juan County, Utah, USA

Abstract

ABSTRACTRedcanyonite (IMA2016-082), (NH4)2Mn[(UO2)4O4(SO4)2](H2O)4, occurs underground in the Blue Lizard mine, Red Canyon, White Canyon district, San Juan County, Utah, USA. It occurs with natrozippeite, brochantite, devilline, posnjakite, johannite, gypsum, bobcookite, pickeringite, pentahydrite and the NH4-analogue of zippeite: ammoniozippeite. Redcanyonite occurs as radial aggregates of red–orange needles and blades individually reaching up to 0.2 mm long, with aggregates measuring up to 1 mm in diameter. Crystals are flattened on {010} and elongated along [100], exhibit perfect cleavage on {010}, and exhibit the forms {010}, {001}, {101} and {10$\bar{1}$}. Twinning is ubiquitous, by 180° rotation on [100]. Redcanyonite is translucent with a pale orange streak, is non-fluorescent, has a Mohs hardness of 2, and has brittle tenacity with uneven fracture. Optically, redcanyonite is biaxial (+), α = 1.725(3), β = 1.755(3), γ = 1.850(5) (white light); 2V (meas.) = 60(2)°, 2V (calc.) = 61.3°; and dispersion isr<v, very strong. Pleochroism is:X= orange,Y= yellow andZ= orange;Y<<X<Z. The optical orientation isX=b,Y≈c*,Z≈a. The empirical formula is (NH4)2.02(Mn0.49Cu0.09Zn0.06)Σ0.64H+0.72[(UO2)4O4(S0.99P0.01O4)2](H2O)4, based on 4 U and 24 O apfu. Redcanyonite is monoclinic,C2/m,a= 8.6572(17),b= 14.155(3),c= 8.8430(19) Å, β = 104.117(18)°,V= 1050.9(4) Å3andZ= 2. The structure was refined toR1= 0.0382 for 1079 reflections withIobs> 3σI. Uranyl oxo-sulfate sheets in redcanyonite adopt the well-known zippeite topology, which consists of zigzag chains of uranyl pentagonal bipyramids linked by sulfate tetrahedra to form sheets. The sheets are linked to each other through bonds to interlayer NH4+groups and octahedrally coordinated Mn2+, and by hydrogen bonds from H2O groups. Redcanyonite is named for Red Canyon in southeast Utah, USA.