Acicular Aggregates Research Articles

Кинетические параметры процесса термического разложения нанопорошка гидроксида кобальта при изотермических условиях

The paper focuses on the kinetic parameters of synthesizing Co3O4 nano-powder by thermal decomposition of hydroxide Co(OH)2 under isothermal conditions. The thermal decomposition of Co(OH)2 nano-powder under isothermal conditions was carried out in a tube furnace in the temperature range from 150 to 200 °C. Findings of research show that the thermal decomposition rate constant at 200 °C is approximately 2.7 times higher than that at 150 °C. Accordingly, for 80 min of thermal decomposition, the process accelerates 1.8 times. The activation energy of this process is approximately 33 kJ/mol, which indicates a mixed reaction mode. The study shows that Co3O4 nanoparticles obtained at the temperature of the maximum thermal decomposition rate, i.e. 180 °C, mainly consist of elongated ovoid and acicular aggregates with an average particle value of 47 nm and the length of up to 200 nm.

Minerals of the Alunite Supergroup in Ores Diagenites of the Yaman-Kasymassive Sulfide Deposit (South Urals)

Minerals of the alunite supergroup (alunite, plumbogummite, hinsdalite, crandallite) were found in ore diagenites of the Yaman-Kasy massive sulfde deposit, South Urals. Numerous spheroids (up to 20 μm) of these minerals with radial and zoned structure and acicular aggregates in assemblage with quartz, chlorite, and hematite are found in chalcopyrite, which replaced fragments of pyrite, marcasite and sphalerite during diagenesis, or in quartz-chlorite matrix. The minerals contain (wt. %): 7.16–19.81 P2O5, 0.93–8.77 CaO, 1.15–33.05 PbO, 1.21– 9.94 Fe2O3, 0.05–3.38 BaO and 0.2–2.51 ZnO. The Pb (plumbogummite, hinsdalite) and Ca (crandallite) members of the alunite supergroup are dominant in hematite-bearing diagenites, whereas K member (alunite) occurs in sphalerite-chalcopyrite diagenites associated with chlo-ritolites. The fnds of these minerals in products of submarine supergenesis of massive sulfde ores expand our knowledge on their areas of occurrences. Figures 7, Tables 1, References 19.

Horákite, a new hydrated bismuth uranyl-arsenate-phosphate mineral from Jáchymov (Czech Republic) with a unique uranyl-anion topology

Horakite, ideally (Bi7O7OH)[(UO2)4(PO4)2(AsO4)2(OH)2]·3.5H2O, is a new uranyl mineral discovered on a specimen originating from Jachymov, Czech Republic (most probably from the Geister vein, Rovnost mine). It occurs as a su-pergene alteration mineral in association with phosphuranylite (overgrowing older metatorbernite–metazeunerite) in a quartz gangue with abundant tennantite. Horakite forms greenish-yellow to pale yellow prismatic crystals clustering to acicular aggregates, up to 1 mm across. Crystals are transparent to translucent with a vitreous luster. The mineral has a light yellow streak. Estimated Mohs’ hardness is ~2. The cleavage is perfect on {100}. The calculated density is 6.358 g/cm3. Horakite is optically biaxial (+), alpha =approx 1.81, beta =approx 1.84, gamma =approx 1.88 (measured in white light); 2Vobs. is 78(1)°, 2Vcalc. is 83°; non-pleochroic. The optical orientation is X = b, Z =approx.c. Electron-microprobe analysis yielded the empirical formula (Bi7.01Pb0.14)O7OH[(U1.01O2)4(P1.03O4)2(As0.74Si0.23O4)2(OH)2]·3.5H2O based on 37.5 O apfu. Horakite is monoclinic, C2/c, a = 21.374(2), b = 15.451(3), c = 12.168(2) A, beta = 122.26(1)° and V = 3398.1(10) A3, Z = 4. The eight strongest X-ray powder-diffraction lines are [dobs A(I)(hkl)]: 11.77(100)(110), 6.21(23)(–202), 5.55(23)(310, –112), 4.19(27)(–331), 3.54(61)( 510, –423), 3.29(20)( 331), 3.14(58)(241, 023) and 3.02(98)(150, 113, –533, mult.). The crystal structure refinement of horakite, refined to R = 5.95 % for 1774 unique observed reflections, revealed a novel sheet structure. It consists of topologically unique [(UO2)4(PO4)2(AsO4)2(OH)2] sheets (i.e., horakite topology), and an interstitial {(Bi7O7OH)(H2O)3.5} complex. Sheets result from the polymerization of UO7 bipyramids by sharing edges to form tetrameric units; tetrahedrally coordinated sites are linked to the UO7 both monodentately (T1 to U1) and bidentately (T2 to U2). The mineral is named after Frantisek Horak (1882–1919), the mining engineer in Jachymov, and his grandson, Vladimir Horak (born 1964), an amateur mineralogist and expert on the mining history of the Jachymov ore district.

Effects of solvent vapor annealing on organic photovoltaics with a new type of solution-processable oligothiophene-based electronic donor material

We synthesized a pair of A–D–A–D–A (A = acceptor, D = donor unit) oligomers containing a benzothiadiazole (BT) unit, namely, DRCN5BT-HH and DRCN5BT-TT, which differs in the positions of alkyl side chains. Solution-processed bulk heterojunction solar cells consisting of PC61BM and DRCN5BT-HH gave a high Voc of 1.10 V and markedly improved power conversion efficiencies up to 3.26% after solvent vapor annealing (SVA). The effects of SVA on the morphology and microstructure of the active layer were investigated by atomic force microscopy (AFM) and grazing-incidence wide angle X-ray scattering (GIWAXS). For DRCN5BT-HH, crystallization, orientation, and molecular ordering were improved, and a fibrillar structure was formed with acicular aggregates of the donor. For DRCN5BT-TT, no marked structural changes were induced by SVA. We found that these morphological and microstructural changes induced by SVA correlate with the differences in the photovoltaic properties of both of the isomers.

Mathesiusite, K5(UO2)4(SO4)4(VO5)(H2O)4, a new uranyl vanadate-sulfate from Jachymov, Czech Republic

Mathesiusite, K5(UO2)4(SO4)4(VO5)(H2O)4, a new uranyl vanadate-sulfate mineral from Jáchymov, Western Bohemia, Czech Republic, occurs on fractures of gangue associated with adolfpateraite, schoepite, čejkaite, zippeite, gypsum, and a new unnamed K-UO2-SO4 mineral. It is a secondary mineral formed during post-mining processes. Mathesiusite is tetragonal, space group P4/n, with the unit-cell dimensions a = 14.9704(10), c = 6.8170(5) Å, V = 1527.78(18) Å3, and Z = 2. Acicular aggregates of mathesiusite consist of prismatic crystals up to ~200 μm long and several micrometers thick. It is yellowish green with a greenish white streak and vitreous luster. The Mohs hardness is ~2. Mathesiusite is brittle with an uneven fracture and perfect cleavage on {110} and weaker on {001}. The calculated density based on the empirical formula is 4.02 g/cm3. Mathesiusite is colorless in fragments, uniaxial (-), with ω = 1.634(3) and ε = 1.597(3). Electron microprobe analyses (average of 7) provided: K2O 12.42, SO3 18.04, V2O5 4.30, UO3 61.46, H2O 3.90 (structure), total 100.12 (all in wt%). The empirical formula (based on 33 O atoms pfu) is: K4.87(U0.99O2)4(S1.04O4)4(V0.87O5)(H2O)4. The eight strongest powder X-ray diffraction lines are [dobs in Å (hkl) Irel]: 10.64 (110) 76, 7.486 (200) 9, 6.856 (001) 100, 6.237 (101) 85, 4.742 (310) 37, 3.749 (400) 27, 3.296 (401) 9, and 2.9409 (510) 17. The crystal structure of mathesiusite was solved from single-crystal X-ray diffraction data and refined to R1 = 0.0520 for 795 reflections with I > 3σ(I). It contains topologically unique heteropolyhedral sheets based on [(UO2)4(SO4)4(VO5)]5- clusters. These clusters arise from linkages between corner-sharing quartets of uranyl pentagonal bipyramids, which define a square-shaped void at the center that is occupied by V5+ cations. Each pair of uranyl pentagonal bipyramids shares two vertices of SO4 tetrahedra. Each SO4 shares a third vertex with another cluster to form the sheets. The K+ cations are located between the sheets, together with a single H2O group. The corrugated sheets are stacked perpendicular to c. These heteropolyhedral sheets are similar to those in the structures of synthetic uranyl chromates. Raman spectral data are presented confirming the presence of UO22+, SO4, and molecular H2O.

The Bi sulfates from the Alfenza Mine, Crodo, Italy: An automatic electron diffraction tomography (ADT) study

We report about three bismuth sulfates from mineralized quartz dikes from Alfenza (Crodo, Italy), two new phases and a rare mineral, cannonite, all growing on bismuthinite. The first new phase occurs as white, “hortensia-like” aggregates of pseudo-hexagonal platelets, with perfect basal cleavage, ~20 μm wide and few micrometers thick. The approximate composition is Bi 2 O 2 (SO 4 ), and cell parameters and symmetry, as determined by automatic diffraction tomography, are a = 22.0(4), b = 16.7(3), c = 15.9(3) A, β = 102.9(5)°, space group Pc or P 2/ c . A major stacking disorder is detected by HR-SEM images and electron diffraction data. The second new phase was detected only by TEM. It can be distinguished by its random orientation on the TEM grid (i.e., absence of preferential parting), the higher resistance under the electron beam, and different cell parameters and structure, whereas the composition is similar (Bi/S ~ 2.2/1), apart for the presence of tellurium up to ~6 cations percents. The unit cell is hexagonal, space group P 62 c , a = 9.5(2) and c = 15.4(3) A. In this case, a structure model was obtained ab initio from electron diffraction data. Interestingly, the mineral has a porous structure with one dimensional porosity (diameter of the channel ~7 A). Finally, within the same centimeter sized hand-specimens, we detected also cannonite. Its identification was done by automatic diffraction tomography. The measured cell parameters are a = 7.7(2), b = 13.9(3), c = 5.7(1) A, β = 109.8(5)°, the space group P 2 1 / c . Cannonite at Alfenza forms radiating, acicular aggregates of colorless, transparent crystals with “scalpel-like” habit, elongated along c , up to 200 μm in length.

Cannonite [Bi2O(SO4)(OH)2] from Alfenza (Crodo, Italy): crystal structure and morphology

AbstractCanonite from Alfenza grows as crowded, radiating, acicular aggregates covering bismuthinite crystals. Individual crystals have a lozenge-shaped habit on {010}, the presumed cleavage plane of cannonite. Crystal structure refinements in the P21/c space group of two single crystals led to the following cell parameters: a = 7.7196(5) Å, b = 13.8856(9), c = 5.6980(4), b = 109.174(1)º (R1 = 0.0424); and a = 7.7100(8), b = 13.8717(14), c = 5.6939(6), b = 109.155(2)º (R1 = 0.0438). Hydrogen atoms were also localized in the density-difference Fourier map and refined with soft restraints on the bond distances. Raman and IR spectroscopy confirm the presence of OH groups and the absence of molecular water, and deliver OH···O geometry wholly comparable with the structure refinement. Electron microprobe analyses revealed no significant levels of elements other than those expected in the ideal formula except fluorine which was present up to 0.14 a.p.f.u. The crystal structure can be described in terms of anion-centred OBi4 edge-sharing tetrahedra forming chains running parallel to z and strongly cemented along x by isolated SO4 tetrahedra. Each OBi4 tetrahedron is further connected along y by OH groups, making walls of composition Bi4O2(SO4)2(OH)4 parallel to (010). These walls are tied to each other along y by fewer Bi–O–S bridges and weaker OH···O bonds.

Ultrastructural Evidence for a Novel Accumulation of Ca in a Microbial Mat from a Slight Acidic Hot Spring

Abstract:Microbial mats are ecosystems that can control or induce the precipitation of calcium (Ca) carbonate on Earth through geological time. In the present study, we report on a novel accumulation of Ca, together with iron (Fe), in a microbial mat collected from a slight acidic hot spring (pH=5.9) in south China. Combining an array of approaches, including environmental scanning electron microscopy, X‐ray microanalysis, transmission electron microscopy, and selected area electron diffraction, we provide ultrastructral evidence for amorphous acicular aggregates containing Ca and Fe associated with cyanobacteria precipitating in the microbial mats. Cyanobacterial photosynthesis and exopolymeric organic matrixes are considered to be responsible for the precipitation of Ca. These amorphous acicular aggregates might imply the early stage of calcification occurring in microbial mats. Ca and Fe coprecipitation indicates another potential important way of inorganic element precipitation in hot spring microbial mats. Our results provide insight into the possible mechanism of cyanobacterial calcification and microfossil preservation in slight acidic hot spring environments.

The geogene and anthropogenetic impact on the formation of per descensum vivianite–goethite–siderite mineralization in Mesozoic and Cenozoic siliciclastic sediments in SE Germany

Different types of Fe mineralization developed during the post-glacial period by per descensum processes (mineralization deposited near-surface by the descending meteoric waters) in the topmost parts of the NE Bavarian basement and its foreland sediments. These ferricretes sensu lato contain mainly vivianite, some goethite and siderite. They were investigated by means of SEM-EDX, XRD, and XRF and examined under the petrographic and ore microscope. The age of formation of these ferricretes was determined by radiocarbon and optical stimulated luminescence dating. Based upon these age data, morphological differences and their mineralogical and chemical compositions, two different types of ferricretes were established in the study area. Type-I in the topmost part of the alluvial fan deposits is older than 6000 BC and of geogene origin only. Type II was formed between 645 and 875 AD in the regolith on the crystalline basement rocks. It was caused by geogene and anthropogenic processes, when the first settlers in this area began smelting iron ore. Vivianite is also a common mineral of the ironstone deposits in the Cretaceous foreland sediments and of vein mineralization in crystalline basement rocks near the ferricretes under study. Post-glacial per descensum vivianite mineralization in ferricretes may be distinguished from these older per ascensum (mineralization formed at shallow depth or deeper from circulating hydrothermal fluids mainly along fissures and fault zones) vivianite mineralization by their micromorphology (stellar and acicular aggregates). All ferricretes under study developed under temperate humid climatic conditions in a narrow physico–chemical setting. This interpretation is based on (1) age dating, (2) correlation with data from the literature, (3) calculation of the stability fields of authigenic minerals involved in the development of these ferricretes. The pH values of the mineralizing fluids fluctuated between pH 5 and 9, with an Eh ≤ 0. These post-glacial ferricretes abundant in vivianite represent the initial and proximal facies of continental ironstones which are widespread in Mesozoic and Cenozoic sedimentary series in Central Europe.

Interfacial electrostatics guiding the crystallization of CaCO3 underneath monolayers of calixarenes and resorcarenesElectronic supplementary information (ESI) available: representative optical and scanning electron micrographs of CaCO3 crystals grown underneath a monolayer of 1 at low surface pressure; additional crystallographic data including numbering schemes, tables and refinement details. See http://www.rsc.org/suppdata/jm/b4/b403132f/

The amphiphilic octaacids rccc-4,6,10,12,16,18,22,24-octakis-O-(carboxymethyl)-2,8,14,20-tetra(n-undecyl)resorc[4]arene (1) and 5,11,17,23,29,35,41,47-octakis(1,1,3,3-tetramethylbutyl)-49,50,51,52,53,54,55,56-octa(carboxymethoxy)calix[8]arene (2) form stable monolayers at the air–water interface which induce growth of CaCO3 crystals at the monolayer–solution interface. Uniformly (012) oriented rhombohedral calcite single crystals grow underneath a monolayer of 2, whereas crystallization under a monolayer of 1 preferentially leads to formation of acicular aggregates of aragonite crystals. While polymorph selection and orientations of the CaCO3 crystals critically depend on the average charge density of the monolayer, the molecular shape and the particular Ca coordination behaviour of the amphiphiles that form the monolayer are of minor importance. CaCO3 crystal growth underneath monolayers of macrocyclic amphiphiles is briefly reviewed and the present experimental observations are compared to previous related investigations on “template-induced” biomimetic mineralization.

GLADIUSITE, Fe3+2(Fe2+,Mg)4(PO4)(OH)11(H2O), A NEW HYDROTHERMAL MINERAL SPECIES FROM THE PHOSCORITE CARBONATITE UNIT, KOVDOR COMPLEX, KOLA PENINSULA, RUSSIA

Gladiusite, ideally Fe 3+ 2 (Fe 2+ ,Mg) 4 (PO 4 )(OH) 11 (H 2 O), monoclinic, a 16.959(2), b 11.650(3), c 6.266(6) A, β 90.00(5)°, V 1238(1) A 3 , space group P 2 1 / n , Z = 4, is a new mineral species from hydrothermal assemblages associated with the phoscorite–carbonatite unit of the Kovdor alkaline-ultramafic complex, Kola Peninsula, Russia. It occurs in vugs within veins of mineralized dolomite carbonatite. Associated minerals are dolomite, pyrochlore, several generations of magnetite, pyrite, rutile, a ternovite-like phase, catapleiite, bobierrite, rimkorolgite, juonniite, strontiowhitlockite, collinsite (including a Sr-rich variety) and chlorite. Gladiusite occurs as acicular aggregates and as free-standing radial clusters ( 3 , respectively. Gladiusite is biaxial negative and strongly pleochroic, α 1.722(2), β 1.730(2), γ 1.737(2), 2 V calc. = 78.3°. The strongest reflections in the X-ray powder-diffraction pattern [ d in A( I )( hkl )] are: 9.61(53)(110), 6.87(77)(210), 5.83(89)(020), 4.805(100)(220), 3.787(62)(130), 3.533(84)(230), and 2.868(66)(140). Electron-microprobe analysis and Mossbauer spectroscopy gave (wt.%) FeO 25.00, Fe 2 O 3 29.90, MgO 11.16, MnO 0.78, P 2 O 5 12.46, TiO 2 0.04, H 2 O(calc.) = 20.18, sum = 99.51 wt.%; the H 2 O content, obtained by the Penfield method, is 19.7 wt.%. The unit formula is Fe 3+ 2.00 [Fe 2+ 2.02 Mg 1.61 Fe 3+ 0.17 Mn 2+ 0.06 ] ∑3.86 (P 1.02 O 4 )(OH) 11 (H 2 O) on the basis of 16 O atoms. The simplified formula is Fe 3+ 2 (Fe 2+ ,Mg) 4 (PO 4 )(OH) 11 (H 2 O). Crystal-structure study showed gladiusite to be extensively twinned on [001]. Gladiusite is considered to be a product of hydrothermal alteration of pyrrhotite and fluorapatite, the primary Fe and P minerals in the dolomite carbonatite. The mineral is named in accordance with the morphology of the crystals, which resemble double-edge swords ( gladius , in Latin) in SEM images.

Nonclassical decomposition products of austenite in Fe-C-Cr alloys

Unusual austenite decomposition products in two Fe-0.4C alloys containing chromium additions of 3.5 and 10 wt pct have been studied. Detailed transmission electron microscopy (TEM) has been carried out on partially transformed specimens in order to determine the identities and morphologies of the phases and the mode of formation. The most descriptive terms for these novel products are spiky pearlite and acicular ferrite/carbide aggregates. The spiky pearlite is distinguished by its nonnodular transformation front and by the presence of individual segments or units composed of ferritesheathed carbides. The acicular aggregates appear as dark-etching, macroscopic plate-shaped structures that are formed from the successive nucleation of these single ferrite/carbide subunits, which are crystallographically related to the austenite grain in which they grow, with a predominant orientation. The uniqueness of these structures has been reinforced by the detection of customary pearlite in both of the alloys and by the presence of classical upper and lower bainites in the low-chromium alloy. It is proposed that the structures develop as a result of the oriented coupled growth of the individual ferrite/carbide segments identified by the study.

Tourmaline in a sub-Cambrian palaeosol on the Proterozoic Lewisian rocks of NW Scotland

Tourmaline, not hitherto recorded in Lewisian rocks of Sutherland, nor reported as a secondary mineral in Precambrian palaeosols, occurs in a late Proterozoic, sub-Cambrian palaeosol in NW Scotland. From field and petrological criteria, the tourmaline is secondary and peculiarly associated with the alteration profile. Hence, it formed either during weathering or later in the profile’s history. A minor constituent of the palaeoregolith immediately below the unconformity, the tourmaline mostly occurs as sub-millimetre, radiating, acicular aggregates and is schorl in composition. Black, tourmaline+quartz veinlets cross-cut the profile. Stable isotope and fluid inclusion data suggest that the tourmaline formed from surface-derived fluids at c. 110ºC. It is concluded that boron was adsorbed onto precursor illitic clays of the soil profile during the Cambrian marine transgression. Thus the tourmaline formed subsequently after burial under the sedimentary pile, probably during the Caledonian orogeny, when temperatures were high enough to allow its formation at suitable sites of nucleation, e.g. adjacent to biotite. Its peculiarity as a palaeosol phase is due to the combination of a marine transgression over an exposed, permeable illitic soil and underlying regolith, followed by increase in temperature suffcient to allow the tourmaline to form.

Diversity of iron and silica precipitation by microbial mats in hydrothermal waters, Iceland: Implications for Precambrian iron formations

Direct examination of microbial mats from Icelandic hot springs with transmission electron microscopy and energy-dispersive X-ray spectroscopy revealed a consortium of bacterial cells in varying stages of mineralization. Differences in observed mineralogy largelyreflectdifferencesinthechemistryofthehydrothermalwaters.Silica-richspheroids formedepicellularlyoncellwallsandsurroundingsheathsandcapsulesofmicroorganisms and,insomecases,intracellularlywhenpresumablythecell(s)hadlysed.Commonly,these precipitateswereobservedcoalescingtoformamatrixofamorphoussilicathatcompletely encapsulated the cells and/or replaced their cytoplasmic material. However, in other cells, the precipitates were composed of amorphous granules made exclusively of iron and silica inapproximatelyequalproportions.Atonelocality,thebacteriaformedseveralepicellular iron minerals, ranging from iron-mineralized capsules tofine-grained spheroids of amorphous ferric hydroxide and acicular aggregates of goethite. The complete encrustation of bacterial cells by silica, iron, or a combination of both may greatly enhance their preservation potential, such that these mineralized microorganisms may conceivably represent future microfossils. Thus, we may be witnessing contemporaneous biomineralization processes that are similar to those of the geologic past, particularly with regard to the origin of some Precambrian banded iron formations.

Jeppeite, a new K-Ba-Fe titanate from Walgidee Hills, Western Australia

AbstractJeppeite, a new mineral, similar in composition to and overgrown on priderite, has been found in the lamproite plug of Walgidee Hills (18° 19′ S, 124° 51′ E), Western Australia. The mineral is named for the discoverer, Dr J. Jeppe. It is monoclinic, C2/m, a 15.453 b 3.8368 c 9.123 Å β 99.25°, strongest powder lines 4.50(002) (4), 3.07(310) (10), 2.99(003,31) (10), 2.961(20) (4), 2.812(311,112) (10), 2.091 (6), 2.074 (6), 1.919 (8) similar to artificial K2Ti6O13. The sparse eluvial crystals are black, elongated along b, bounded by {100}, {20} faces (Λ 45°) and {010}; perfect 100 and good 20 cleavages or partings, submetallic lustre, pale-brown streak, brittle, and cleave into (100) flakes. Dobs 3.94, Dcalc 3.98. Colour values for illuminant C from reflectance spectra for Rp, Rb, and Rθ are: Y% 13.3, 14.4, 16.6; λd 474, 473, 475; and Pe% 5.1, 4.5, 4.3. Refractive indices from reflectances at 590 nm in air are 2.13, 2.21 and 2.35. In thin section, αΛα10° blue, β = b dark greenish brown almost to black, γ = c brown. Bireflectance and birefringence positive. H 5–6, VHN100 orientation dependent; for indentations normal to b 664–773.Jeppeite is common in the lamproite as prismatic to acicular aggregates associated with priderite, richterite, shcherbakovite, wadeite, perovskite, and apatite in a green and white celadonite and chlorite matrix, with a little calcite and sphene, after olivine, pyroxene, and leucite.Electron probe analysis, using Fe, Ti, nepheline, and benitoite standards, gave K2O 8.47, BaO 17.35, TiO2 69.29, Fe2O3 (total Fe) 4.74, sum 99.85%; (Mg, Na, Zr detected). This analysis calculates to (K1.15,Ba0.73)Σ1.88 (Ti5.56, Fe3+0.38)Σ5.94O13, or ideally, (K,Ba)2(Ti,Fe)6O13.

Ardaite—a new lead-antimony chlorosulphosalt

AbstractThe first occurrence of new mineral ardaite (a chlorine sulphosalt) has been discovered in the Madjarovo polymetallic ore deposit (Bulgaria). The average composition is Pb 56.50, Ag 0.04, Sb 22.48, S 15.56, Cl 3.78, total 98.36 wt.%. The formula is Pb20–18 Sb12–24S34–36.5Cl6–8. The mineral occurs as fine acicular aggregates associated with galena, nadorite, a Cl-bearing robinsonite and Cl-beating semseyite, pyrostilpnite, silver- bearing tetrahedrite and anglesite.