Optical Orientation Research Articles

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

Abstract 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).

Polarized optical properties in liquid crystals devices with photoaligned metal nanoparticle gratings

Liquid crystals (LCs) alignment can be controlled by the local enhanced light fields of the metallic nanostructures in the localized surface plasmonic resonant (LSPR) state. Here, a nanostructured metallic grating patterns with groove widths of 180 nm is introduced to align the nematic LC molecules on the glass prism surface to construct the reflective hybrid LC cell accompanied by a rubbed ITO glass slide. Using the polarized light microscopy (PLM) characterization, the optical orientation effect of the silver nanostructured grating patterns on nematic LCs has been investigated. As a result, the silver nanostructured grating patterns has been found to regulate the orientation of the LC molecules when illuminated by linearly polarized white light and determine the light transmission and reflection. The results demonstrated that the silver nanostructured grating patterns serves for the topological alignment of LCs which is usually aligned by the rubbed substrate. Thus, our hybrid LC cell with topological rubbing and light controlled variation of LCs alignment could provide new opportunities for photonic applications.

Frame Deletion Detection Based on Optical Flow Orientation Variation

Frame deletion detection is an arrestive field for video forensics in recent years. This paper presents a frame deletion detection algorithm based on optical flow orientation variation. Optical flow field has been proved to be effective for the detection of the frame deletion operation. However, current optical-flow based methods have relatively poor detection performance for real-world videos. Our research aims to develop a new forensic method to detect frame deletion for real-world videos. The proposed algorithm firstly develops an analytical model for flow orientation variation between adjacent optical flow fields, and exhibits a novel forensic clue for frame deletion detection, under an ideal but reasonable assumption. Accordingly, an effective descriptor, namely pseudo flow orientation variation (PFOV), is created to approximate the flow orientation variation, as a discriminative description feature to capture the frame deletion trace. The Frobenius norm and a smooth function are also introduced to quantify each descriptor to form an one-dimensional time series, and further statistics technique is adopted to detect the anomalous points in the time series caused by frame deletion. In addition, to improve the descriptor performance, the Robust Principal Component Analysis (RPCA) is applied to extract moving objects from video sequences and compute the proposed descriptor on them. The tests are made on 324 real-world videos, and experiment results demonstrate that the true positive rate can reach 90.12%, meanwhile the false alarm rate is 7.71%, which indicates the superiority of the proposed method in the forensic algorithms for real-world video.

Microstructural and mechanical characterisation of Al-Zn-Mg-Cu alloy processed by multi-directional cryo-forging

Aim of the present investigation is to study the microstructural and mechanical properties of Al-Zn-Mg-Cu alloy before and after multi-direction forging (MDF) at cryogenic condition up to 3 cycles. Microstructure evolution of specimen was examined using optical microscope and orientation imaging microscopy as well as X-ray diffraction. Mechanical properties were measured by tensile test and Vickers micro hardness. Microstructural investigation shows that after 3 cycle of MDF average grain size was reduced to 8 µm with low angle grain boundaries (LAGBs) and high dislocation density. Mechanical examination displays an improvement in hardness, yield strength and ultimate tensile strength is due to increases in grain boundaries and strain hardening effect. After 3 cycles of MDF process with cumulative strain ΣΔε = 3.64 led to the formation of fine grain structure, and microhardness were observed to be 168 HV.

Improvement of Optical Tracking-Based Orientation Estimation by Fusing Gyroscope Information

Optical tracking systems (OTS) can provide high position accuracy over a large workspace. However, the orientation from the OTS is related to the distance between markers, which contains large errors when the distance is small or line-of-sight problems occur. The orientation estimation with a gyroscope is complementary to the OTS-based orientation. In this article, an error-state Kalman filter (ESKF) is proposed to fuse them. Two experiments were performed to verify the performance: first, a unit including markers and a gyroscope was placed statically and rotated dynamically in 3-D space. Secondly, two units were used to estimate the relative orientation between the hand and fingers. The static and dynamic orientation errors reduced from 0.39° ± 0.16° and 2.75° ± 1.56° to 0.23° ± 0.02° and 1.50° ± 0.62°, respectively, when the distance between markers was 13 mm. The second experimental results show that the fused method improved the OTS performance by smoothing the estimate, filling the relative orientation during the line of sight period, and correcting the estimation when there were identification problems of markers.

Petrofabric and geochemical features of ultramafic rocks on the example of restite metamorphites of the Kuznetsk Alatau (Western Siberia), olivine cumulates of the Yoko-Dovyren layered massif (Northern Cisbaikalia) and their analogues from ultrabasic xenoliths of the Canary Islands (Spain)

The article presents the results of petrostructural and mineralogical studies of olivine grains from ultrabasic and basic rocks of different genesis. In particular, they correspond to cumulative dunites of the Yoko-Dovyren layered massif (Northern Cisbaikalia), restite hyperbasites of the Velvet massif (Kuznetskiy Alatau), and xenoliths of peridotites from basalts of the Canary Islands (Spain). The relationship between the petrostructural and mineralogical features of ultrabasic rocks is shown, which makes it possible to identify their cumulative and restite varieties. An important element of the petrostructure of ultrabasites is the orientation of olivine, which reflects either the conditions for the formation of primary crystals in the magmatic melt, or the conditions for its recrystallization as a result of plastic deformations during exhumation to the Earth's surface. The mineral composition of rocks is an additional feature that reflects the real conditions of formation. In the presence of basic plagioclase, it is already quite difficult to speak about the restitic nature of these ultrabasic rocks. On the other hand, plastic deformations of olivine are characteristic of restitic hyperbasites, in which plagioclase is absent. The results of mineralogical studies in ultrabasic xenoliths of the Canary Islands showed the presence of basic plagioclase (labradorite), as well as chrysolite-type olivine (12-16 Fa), which corresponds to the attributes of ultrabasic layered intrusions such as the Yoko-Dovyren dunite-troctolite-gabbro pluton. For restite hyperbasites (by the example of the Kuznetsk Alatau), the iron content of olivine does not exceed 9-10% of the fayalite end, while plagioclase and clinopyroxene are absent. A characteristic feature of the xenoliths of the Canary Islands is the presence of endiopside, which is present in layered intrusions, but is absent in the restrained fragments of the upper and lower mantle. It is assumed that the xenoliths in the basalts of the Canary Islands are not of a mantle nature, but are fragments of a deep magma chamber. The studies of the optical orientation of olivine in xenoliths of the rocks of Lanzarote Island confirm these conclusions. The geochemical parameters of ultramafic xenoliths on Tenerife Island may well correspond to deeper formations.

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.

POTENTIALS OF MINI-INVASIVE ENDORHINOSURGERY TAKING INTO ACCOUNT THE ACTUAL BOUNDARIES OF THE FIELD OF VIEW OF MODERN ENDOSCOPES

One of the predetermining factors to perform minimally invasive rhinosurgery successfully is the searching for optimal surgical access areas, the choice of which at present mostly depends on the visualization capabilities of endoscopic devices. The angular vision is one of the important factors for planning and performing endonasal interventions on the anterior maxillary sinus. A large viewing angle allows surgeons to expand the potentials of minimally invasive access, reduce the need to replace endoscopes with different angles during the intervention and improve the quality of the surgical procedure. The purpose of this study was to improve the method for selecting surgical access to the maxillary sinus, taking into the optical axis and the actual size of the field of view provided by the endoscope. The simulation of the process of selecting the optimal option for access to the maxillary sinus on the basis of our own method of predicting the visualization of the lumen in the sinus was performed. To determine the actual viewing angle of the endoscope, we compared the application of the standard methodology and the approach we elaborated. 3 endoscopes with a 70° optical axis orientation were examined; the studies were performed three times. We found that the results of determining the boundaries of the field of view according to our technique and to the method of Wang Q. et al. (2017) did not differ significantly, that indicates the comparable accuracy of both methods. With the declared identical characteristics of all three endoscopes, we revealed the magnitude of the field of view differed quite significantly (by a maximum of 8.7°). Moreover, the value of the viewing angle in all samples of endoscopes tested was greater than that provided by the manufacturer for standard endoscopes (60 °). The average duration of measuring the magnitude of the field of view of the endoscope by the method we proposed took 25.3 ± 3.2 s that was significantly faster than by the method of Wang Q. et al. (2017), 83.7 ± 2.0 s P≤0.05). We should also stress on the greater convenience of carrying out examinations according to our method. When assessing the potential of the maxillary sinus visualization, it is necessary to take into account not only the individual anatomical features of a patient, but also the actual optical characteristics of endoscopes. The device we designed for determining the boundaries of the field of view of endoscopes is easy to manufacture, requires less time for testing and enables to determine the actual viewing angles of the endoscope quicker and more effectively. Actual optical characteristics of endoscopes may differ from the standards.

Frequency shifts of the magnetic resonance of Rb and K atoms in the K-Rb tandem magnetometer

Collisions of alkali atoms in the ground state are accompanied by the exchange of electron polarization between the colliding atoms, which lead to the polarization transfer between particles. As a result of this process, the electronic orientation is transferred from the spin oriented atoms to unpolarized atoms, along with the polarization transfer, the magnetic resonance frequency shifts of polarized atoms occur too. In this work the magnetic resonance frequency shifts of arising from spin exchange collisions in a mixture of alkali potassium and rubidium atoms at the optical orientation of atoms are calculated. The situation when optical pumping by resonant polarized radiation is carried out only for atoms of the one kind is considered. The spin exchange process between alkali atoms was described in the formalism of the complex cross section for spin exchange process. The real and imaginary parts of the complex cross section were calculated using the interaction potentials of alkali atom dimers. The calculation of the frequency shifts is carried out on the basis of data on the interaction potentials for the following pairs of alkali atoms K-K, K-Rb and Rb-Rb. Maxwell averaging of the cross sections over the velocities was done and the temperature dependences of the magnetic resonance frequency shifts for K and Rb atoms were plotted.

Low-Temperature Energy Transfer via Self-Trapped Excitons in Mn2+-Doped 2D Organometal Halide Perovskites

We investigate the mechanisms of energy transfer in Mn2+-doped ethylammonium lead bromide (EA2PbBr4:Mn2+), a two-dimensional layered perovskite (2DLP), using cryogenic optical spectroscopy. At temperature T > 120 K, photoluminescence (PL) is dominated by emission from Mn2+, with complete suppression of band edge (BE) emission and self-trapped exciton (STE) emission. However, for T < 120 K, in addition to Mn2+ emission, PL is observed from BE and STEs. Data further reveal that for 20 K < T < 120 K, STEs form the most dominant routes in assisting energy transfer (ET) from 2DLP to Mn2+ dopants. However, at higher Mn2+ concentration, higher activation energies indicate defect states come into play, successfully competing with STEs for ET both from BE to STE states and from STE to Mn2+. Finally, using polarization-resolved spectroscopy, we demonstrate optical spin orientation of the Mn2+ ions via ET from 2DLP excitons at zero magnetic field. Our results reveal fundamental insights on the interactions between quantum confined charge carriers and dopants in organometal halide perovskites.

Dynamics of Optical Pumping Processes in Coated Cells Filled with Rb Vapour

A better theoretical understanding of the atom – surface interactions and of the experimental consequences and applications to a reproducible method for the construction of reliable coated absorption cells is the main scope of our research. In this paper we report on the influence of diode laser intensity and of diode frequency scanning rate on the spectrum of the D2 line of Rb atoms, contained in paraffin or PolyDiMethylSiloxane (PDMS) coated glass cells. The anti-relaxation coating of inner walls of the glass cells allows to extend the optical orientation of atoms induced by the light to the entire cell volume and atomic velocity distribution. Moreover, in order to further investigate the role of atoms adsorbed in the anti-relaxation coatings, the D2 line spectra are compared for two cases: without and with illumination of the walls of the cell by an ultraviolet lamp. A theoretical model based on rate equations is introduced in order to analyze the experimental results. The extracted behaviour is a simple method to test the conditions of a coated surface. This finds applications in all cases where timely assessment of an organic coating layer is critical, from vapour spectroscopy to magneto-optical trapping of rare and radioactive species.

Real-time modeling of optical orientation in GaAs: Generation and decay of the degree of spin polarization

We present a real-time abinitio description of optical orientation in bulk GaAs due to the coupling with an ultrashort circular polarized laser source. The injection of spin polarized electrons in the conduction band is correctly reproduced, and a non vanishing spin polarization ($\mathbf{P}$) parallel to the direction of propagation of the laser ($z$) emerges. A detailed analysis of the generation and the evolution of $\mathbf{P}(t)$ is discussed. The single $\mathbf{k}$-point dynamics is a motion of precession around a fixed axis with constant $|\mathbf{P}|$ and fixed frequency. Instead, the $\mathbf{k}$-integrated signal shows only a time dependent $P_z(t)$ and decays few pico seconds after the end of the laser pump due to decoherence. Decoherence emerges since the individual contributions activated by the pump give rise to destructive interference. We interpret the results in terms of the \emph{free induction decay} mechanism proposed some years ago. For the first time we are able to reproduce such effect in a full abinitio fashion, giving a quantitative estimate of the associated decay time. Our result also shows a possible explanation to the time decay of spin magnetization observed in many real-time abinitio simulations.

Optical orientation, polarization pinning, and depolarization dynamics in optically confined polariton condensates

We investigate the optical orientation, polarization pinning, and depolarization of optically confined semiconductor exciton-polariton condensates. We perform a complete mapping of the condensate polarization as a function of incident nonresonant excitation polarization and power. We utilize a ring-shaped excitation pattern to generate an exciton-induced potential that spatially confines polariton condensates into a single mode. We observe that formation of circular polarization in the condensate persists even for a weakly cocircularly polarized pump. By varying the excitation ring diameter we realize a transition from the condensate polarization being pinned along the coordinate-dependent cavity-strain axes, to a regime of zero degree of condensate polarization. Analysis through the driven-dissipative stochastic Gross-Pitaevskii equation reveals that this depolarization stems from a competition between sample induced in-plane polarization splitting and the condensate-reservoir overlap. An increase in the role of the latter results in weakening of the condensate fixed-point phase space attractors, and enhanced random phase space walk and appearance of limit cycle trajectories, reducing the degree of time-integrated polarization.

Magnetic-Resonance Frequency Shifts in a Tandem Cs–K Magnetometer Induced by Spin Exchange

The magnetic-resonance frequency shifts of Cs and K atoms induced by spin exchange at optical orientation of atoms are calculated. The situation under study is characteristic of a tandem magnetometer based on a mixture of cesium and potassium atoms in one working chamber.

Jasonsmithite, a new phosphate mineral with a complex microporous framework, from the Foote mine, North Carolina, U.S.A

Abstract Jasonsmithite (IMA2019-121), Mn42+ZnAl(PO4)4(OH)(H2O)7·3.5H2O, is a pegmatite-phosphate mineral from the Foote Lithium Company mine, Kings Mountain district, Cleveland County, North Carolina, U.S.A. It is interpreted as having formed by late-stage, low-temperature hydrothermal alteration. Crystals are colorless to light brown, slightly flattened prisms to about 1 mm in length with wedge-shaped terminations. The mineral is transparent with vitreous luster, white streak, Mohs hardness 2, brittle tenacity, irregular fracture, and perfect {001} cleavage. The density is 2.63(2) g/cm3. Jasonsmithite is biaxial (–), with α = 1.561(2), β = 1.580(2), γ = 1.581(2), measured in white light. The 2V is 25(5)° and dispersion is r &amp;lt; ν moderate. The optical orientation is Y = b, X ^ c = 18° in obtuse β. The Raman spectrum is dominated by vibrational modes of PO4 and ZnO4 tetrahedra, AlO6 and MnO6 octahedra, and OH groups. Electron microprobe analyses gave the empirical formula (Mn3.09Fe0.87)Σ3.96Zn1.05Al0.98(PO4)4(OH)(H2O)7·3.5H2O. The mineral is monoclinic, P21/c, a = 8.5822(3), b = 13.1770(6), c = 20.3040(14) Å, β = 98.485(7)°, V = 2271.0(2) Å3, and Z = 4. The structure (R1 = 0.0443 for 3685 I&amp;gt;2σI reflections) contains zigzag chains of edge-sharing MnO6 octahedra that corner-link to adjacent chains and to PO4 tetrahedra to form sheets, which are decorated by ZnO4 tetrahedra. The sheets are linked to one another via dimers of AlO6 octahedra, forming a framework with large channels containing H2O groups. With H2O groups removed, the framework has a void space of 70.2% per unit cell, and a framework density of 14.5 polyhedral atoms/1000 Å3, which would place jasonsmithite among the most porous minerals.

Optical alignment of achiral nanoparticles via the use of induced chiral force

A chiral force was found to be induced upon rotation of planar nanoparticles under irradiation of linearly polarized light. The chiral force arises due to differing absorptions of left and right circularly polarized light, correlating with the circular dichroism (CD) of rotated nanoparticle. Charge distribution profiles, which arises from the excited localized surface plasmon polaritons induced by the light, can be used to predict the CD. This offers a simple method of using charge distributions to predict the dynamics of nanoparticles for optical alignment and orientation in the fabrication of various optical devices.

Spin-Dependent Phenomena in Semiconductor Micro-and Nanoparticles—From Fundamentals to Applications

The present overview of spin-dependent phenomena in nonmagnetic semiconductor microparticles (MPs) and nanoparticles (NPs) with interacting nuclear and electron spins is aimed at covering a gap between the basic properties of spin behavior in solid-state systems and a tremendous growth of the experimental results on biomedical applications of those particles. The first part of the review represents modern achievements of spin-dependent phenomena in the bulk semiconductors from the theory of optical spin orientation under indirect optical injection of carriers and spins in the bulk crystalline silicon (c-Si)—via numerous insightful findings in the realm of characterization and control through the spin polarization—to the design and verification of nuclear spin hyperpolarization in semiconductor MPs and NPs for magnetic resonance imaging (MRI) diagnostics. The second part of the review is focused on the electron spin-dependent phenomena in Si-based nanostructures, including the photosensitized generation of singlet oxygen in porous Si and design of Si NPs with unpaired electron spins as prospective contrast agents in MRI. The experimental results are analyzed by considering both the quantum mechanical approach and several phenomenological models for the spin behavior in semiconductor/molecular systems. Advancements and perspectives of the biomedical applications of spin-dependent properties of Si NPs for diagnostics and therapy of cancer are discussed.

Construction and evaluation of the human behavior recognition model in kinematics under deep learning

To explore the construction and evaluation of the human behavior recognition model in kinematics by deep learning, the convolution neural network (CNN) in the field of deep learning was applied to build the CNN human behavior recognition algorithm model. The image data were collected from the KTH and Weizmann datasets and trained; then, the proposed algorithm was simulated by the TensorFlow platform. The results suggested that in the analysis of recognition effect of kinematic description in two datasets, the accuracy of the histogram of optical flow orientation (HOF) method was the worst in both KTH and Weizmann datasets, while the accuracy of the constructed Visual Geometry Group-16 (VGG-16) algorithm model was the highest. In the analysis of the accuracy of the KTH dataset, the boxing action had the highest accuracy of recognition, and the running action had the lowest accuracy of recognition. The average recognition value of all kinds of actions was 91.93%. In the precision analysis of the Weizmann dataset, the bending and hand waving actions had the most accurate recognition rate, while the running action had the lowest recognition rate.

Effect of electric current on the optical orientation of interface electrons in AlGaAs/GaAs heterostructures

The effect of a lateral electric current on the photoluminescence H-band of an AlGaAs/GaAs heterostructure is investigated. The photoluminescence intensity and optical orientation of electrons contributing to the H-band are studied by means of continuous wave and time-resolved photoluminescence spectroscopy and time-resolved Kerr rotation. It is shown that the H-band is due to recombination of the heavy holes localized at the heterointerface with photoexcited electrons attracted to the heterointerface from the GaAs layer. Two lines with significantly different decay times constitute the H-band: a short-lived high-energy one and a long-lived low-energy one. The high-energy line originates from recombination of electrons freely moving along the structure plane, while the low-energy one is due to recombination of donor-bound electrons near the interface. Application of the lateral electric field of ~ 100-200 V/cm results in a quenching of both lines. This quenching is due to a decrease of electron concentration near the heterointerface as a result of a photocurrent-induced heating of electrons in the GaAs layer. On the contrary, electrons near the heterointerface are effectively cooled, so the donors near the interface are not completely empty up to ~ 100 V/cm, which is in stark contrast with the case of bulk materials. The optical spin polarization of the donor-bound electrons near the heterointerface weakly depends on the electric field. Their polarization kinetics is determined by the spin dephasing in the hyperfine fields of the lattice nuclei. The long spin memory time (> 40 ns) can be associated with suppression of the Bir-Aronov-Pikus mechanism of spin relaxation for electrons.

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

AbstractThe 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, withr&gt;v. The optical orientation isX=b,Y=candZ=a. Isselite is pleochroic, withX= light blue,Y= blue,Z= blue;X&lt;&lt;Z&lt;Y. Electron microprobe analyses give (wt.%): SO311.45(21), MgO 0.31(7), CoO 1.07(14), NiO 9.41(90), CuO 51.29(126), ZnO 1.10(20), H2Ocalc24.21, 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 groupPmn21, with unit-cell parametersa= 6.8070(14),b= 5.8970(12),c= 20.653(4) Å,V= 829.0(3) Å3andZ= 2. The crystal structure of isselite was refined from single-crystal X-ray diffraction data toR1= 0.067 on the basis of 2964 reflections withFo&gt; 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.