Magnesioleydetite and straβmannite, two new uranyl sulfate minerals with sheet structures from Red Canyon, Utah

Abstract

AbstractMagnesioleydetite (IMA2017-063), Mg(UO2)(SO4)2·11H2O, and straβmannite (IMA2017-086), Al(UO2)(SO4)2F·16H2O, are two new minerals from mines in Red Canyon, San Juan County, Utah, USA. Magnesioleydetite occurs in the Markey mine and straβmannite occurs in both the Markey and Green Lizard mines. Both minerals are secondary phases found in efflorescent crusts on the surfaces of mine walls. Magnesioleydetite occurs in irregular aggregates (to ~0.5 mm) of blades (to ~0.2 mm) exhibiting the following properties: transparent to translucent; pale green–yellow colour; vitreous lustre; white streak; non-fluorescent; brittle; Mohs hardness ≈ 2; irregular fracture; one perfect cleavage on {001}; and calculated density = 2.463 g/cm3. Straβmannite occurs in irregular aggregates (to ~0.5 mm) of equant crystals (to ~0.2 mm) exhibiting the following properties: transparent; light yellow–green colour; vitreous to greasy lustre; nearly white streak; bright greenish-blue fluorescence; somewhat brittle, Mohs hardness ≈ 1½; irregular fracture; one good cleavage on {001}; measured and calculated densities of 2.20(2) and 2.173 g/cm3, respectively; optically biaxial (–); α = 1.477(2), β = 1.485(2) and γ = 1.489(2) (white light); 2Vmeas.= 72(2)°; dispersionr>v(slight); orientationY=b,X∧c= 20° (in obtuse β); pleochroism withX= nearly colourless,Y= pale green–yellow andZ= light green–yellow (X<Y<Z). The empirical formulas for magnesioleydetite and straβmannite are (Mg0.56Fe0.26Zn0.11Mn0.01)Σ0.94(U0.99O2)(S1.015O4)2·11H2O and Al1.00Na0.16(U0.99O2)(S1.00O4)2[F0.58(OH)0.42]·16H2O, respectively. Magnesioleydetite is monoclinic,C2/c,a= 11.3513(3),b= 7.7310(2),c= 21.7957(15) Å, β = 102.387(7)°,V= 1868.19(16) Å3andZ= 4. Straβmannite is monoclinic,C2/c,a= 11.0187(5),b= 8.3284(3),c= 26.6727(19) Å, β = 97.426(7)°,V= 2427.2(2) andZ= 4. The structures of magnesioleydetite (R1= 0.016 for 2040I> 2σIreflections) and straβmannite (R1= 0.0343 for 2220I> 2σIreflections) each contain uranyl-sulfate sheets based on the protasite-anion topology.