Allantoin and Natrosulfatourea, Two New Bat-Guano Minerals from the Rowley Mine, Maricopa County, Arizona, USA

ABSTRACT The new minerals allantoin (IMA2020–004a), C4H6N4O3, and natrosulfatourea (IMA2019–134), Na2(SO4)[CO(NH2)2], were found in the Rowley mine, Maricopa County, Arizona, USA, where they occur together in bat guano in association with aphthitalite and urea. Allantoin properties: colorless, transparent, untwinned blades to 0.3 mm; white streak; vitreous luster; brittle; Mohs hardness 1½; conchoidal fracture; good {100} cleavage; 1.72(2) g/cm3 density; biaxial (+) with α = 1.558(2), β = 1.593(2), γ = 1.715(3); 2V = 60(1)°; slight r > v dispersion; optical orientation: Y = b, Z ^ a = 30° in obtuse β. Natrosulfatourea properties: colorless, transparent, untwinned prisms to 0.3 mm; white streak; vitreous luster; brittle; Mohs hardness 1½; irregular fracture; perfect {100} cleavage; 1.97(2) g/cm3 density; biaxial (+) with α = 1.456(2), β = 1.464(5), γ = 1.524(2); 2V = 42(1)°; no dispersion; optical orientation: X = a, Y = c, Z = b. Quantitative chemical analyses could not be obtained for allantoin. Electron microprobe analyses provided the empirical formula Na2.02(S0.98O4)[CO(NH2)2] for natrosulfatourea. Allantoin is monoclinic, P21/c, a = 8.0304(9), b = 5.1596(5), c = 14.8011(18) Å, β = 93.017(7)°, V = 612.41(11) Å3, and Z = 4. Natrosufatourea is orthorhombic, Pbcn, a = 5.5918(4), b = 18.1814(14), c = 6.7179(5) Å, V = 682.98(9) Å3, and Z = 4. The crystal structure of allantoin (R1 = 0.0432 for 1073 I > 2σI) is the same as that reported for the equivalent organic compound. In the structure of natrosulfatourea (R1 = 0.0413 for 785 I > 2σI) NaO6 polyhedra and SO4 tetrahedra form polyhedral layers. The O atom of the CO(NH2)2 (urea) group ligates to two Na atoms and projects into the space between polyhedral layers, linking adjacent layers through hydrogen bonds.

Intrinsic donor-bound excitons in ultraclean monolayer semiconductors

The monolayer transition metal dichalcogenides are an emergent semiconductor platform exhibiting rich excitonic physics with coupled spin-valley degree of freedom and optical addressability. Here, we report a new series of low energy excitonic emission lines in the photoluminescence spectrum of ultraclean monolayer WSe2. These excitonic satellites are composed of three major peaks with energy separations matching known phonons, and appear only with electron doping. They possess homogenous spatial and spectral distribution, strong power saturation, and anomalously long population (>6 µs) and polarization lifetimes (>100 ns). Resonant excitation of the free inter- and intravalley bright trions leads to opposite optical orientation of the satellites, while excitation of the free dark trion resonance suppresses the satellitesʼ photoluminescence. Defect-controlled crystal synthesis and scanning tunneling microscopy measurements provide corroboration that these features are dark excitons bound to dilute donors, along with associated phonon replicas. Our work opens opportunities to engineer homogenous single emitters and explore collective quantum optical phenomena using intrinsic donor-bound excitons in ultraclean 2D semiconductors.

Demagistrisite, the Missing Link in a Polysomatic Series from Lawsonite to Orientite

Demagistrisite, ideally BaCa2Mn3+4(Si3O10)(Si2O7)(OH)4·3H2O, is a new mineral found at the Cerchiara mine (eastern Liguria, La Spezia province, Italy). The ore consists of rhythmic interlaying of braunite-bearing metasediments (5–15 cm thick) and hematite-rich cherts. Demagistrisite occurs in association with cerchiaraite-(Mn), namansilite, noelbensonite, orientite, richterite, ruizite, and saponite in matrix consisting of braunite, calcite, cryptomelane, orthoclase, and quartz. Demagistrisite crystals occur as tightly intergrown blades or as millimeter-sized prisms and needles with square cross-section, typically with irregular terminations, and rarely terminated by a low-angle pyramid. The mineral is orange brown to red brown, streak is beige, and luster is vitreous, translucent to transparent. Fracture is irregular. In thin section, it is orange brown. The mineral is optically biaxial (–) with α 1.805(5), β 1.825(5), γ 1.8305(5) (white light); 2Vmeas 58(5)°, 2Vcalc 54.7°; optical orientation X = c, Y = b, Z = a. Dispersion is very strong, r > v. Pleochroism is strong with X orange yellow, Y red brown, Z red brown; X << Z < Y. It is unreactive in concentrated HCl at room temperature. Thirteen chemical analyses by WDS-EMPA gave the following empirical formula (based on 24 O apfu): (Ba0.69Ca1.25Mn2+0.70Sr0.21Na0.12Mg0.02)Σ2.99(Mn3+3.97Al0.03)Σ4(Si3O10)(Si2O7)(OH)3.87·3.13H2O. The mineral is orthorhombic, space group Amm2, with unit-cell parameters a 16.312(8), b 6.176(4), c 9.075(6) Å, V 914.2(10) Å3, and Z = 2. The seven strongest X-ray powder diffraction lines are [d Å (I%; hkl)]: 16.21 (49; 100), 4.86 (44; 111), 4.34 (56; 102,211), 2.871 (54; 220), 2.731 (100; 511,013), 2.671 (74; 320,113,502), and 2.426 (51; 222,313,611). The crystal structure (R1 = 0.0572 for 1485 reflections with I > 2σI) is based on straight edge-sharing chains of Mn3+-centered octahedra extending along [010], which are bridged by disilicate (Si2O7) and trisilicate (Si3O10) groups, yielding a framework. Cavities within this framework contain two large cation sites. The structure of demagistrisite can be considered transitional between the structures of orientite and noelbensonite. Demagistrisite is named in honor of Leandro de Magistris (1906–1990).

Valley Orientation of Electrons and Excitons in Atomically Thin Transition Metal Dichalcogenide Monolayers (Brief Review)

The main aspects of physical phenomena associated with the optical orientation of the spin and valley degrees of freedom in transition metal dichalcogenide monolayers and in van der Waals heterostructures based on them have been briefly reviewed. Owing to features of the band structure and spin–orbit coupling in such systems, circularly polarized light induces optical transitions in different valleys K+ and K– of the Brillouin zone; consequently, the optical orientation of charge carriers and excitons is accompanied by their valley polarization. The main features of the band structure of transition metal dichalcogenide monolayers, excitonic effects, and results of theoretical studies of the valley orientation of excitons and electrons at one-photon absorption have been reported. The linear–circular dichroism and valley orientation of free charge carriers and excitons at multiphoton absorption have been studied. Effects associated with the trigonal symmetry of monolayers, including the inversion of valley polarization at two-photon transitions and the second harmonic generation, have been discussed. The considered theoretical models have been illustrated by experimental data.

Isselite, Cu6(SO4)(OH)10(H2O)4⋅H2O, a new mineral species from Eastern Liguria, Italy

The new mineral isselite, Cu6(SO4)(OH)10(H2O)4⋅H2O, has been discovered in the Lagoscuro mine, Monte Ramazzo mining complex, Genoa, Eastern Liguria, Italy. It occurs as sprays of blue acicular crystals, up to 0.1 mm long, associated with brochantite and posnjakite. Streak is light blue and the lustre is vitreous. Isselite is brittle, with irregular fracture and good cleavage on {001} and {100}. Measured density is 3.00(2) g/cm3. Isselite is optically biaxial (–), with α = 1.599(2), β = 1.633(2) and γ = 1.647(2) (determined in white light). The measured 2V is 63.6(5)°. Dispersion is moderate, with r > v. The optical orientation is X = b, Y = c and Z = a. Isselite is pleochroic, with X = light blue, Y = blue, Z = blue; X << Z < Y. Electron microprobe analyses give (wt.%): SO3 11.45(21), MgO 0.31(7), CoO 1.07(14), NiO 9.41(90), CuO 51.29(126), ZnO 1.10(20), H2Ocalc 24.21, total 98.84. The empirical formula of isselite, based on Σ(Mg,Co,Ni,Cu,Zn) = 6 atoms per formula unit, is (Cu4.80Ni0.94Co0.11Zn0.10Mg0.06)Σ6.00(S1.06O4.19)(OH)10⋅5H2O. Isselite is orthorhombic, space group Pmn21, with unit-cell parameters a = 6.8070(14), b = 5.8970(12), c = 20.653(4) Å, V = 829.0(3) Å3 and Z = 2. The crystal structure of isselite was refined from single-crystal X-ray diffraction data to R1 = 0.067 on the basis of 2964 reflections with Fo > 4σ(Fo). It shows a layered structure formed by zig-zag {001} layers of Cu-centred polyhedra. Sulfate groups occur in the interlayer along with one H2O group. Isselite is chemically related to redgillite and montetrisaite.