Instalment of the margarosanite group, and data on walstromite-margarosanite solid solutions from the Jakobsberg Mn-Fe deposit, Värmland, Sweden

The margarosanite group (now officially confirmed by IMA-CNMNC) consists of triclinic Ca-(Ba, Pb) cyclosilicates with three-membered [Si3O9]6- rings (3R), with the general formula AB2Si3O9, where A = Pb, Ba and Ca and B = Ca. A closest-packed arrangement of O atoms parallel to (101) hosts Si and B cations in interstitial sites in alternating layers. The 3R layer has three independent Si sites in each ring. Divalent cations occupy three independent sites: Ca in B occupies two nonequivalent sites, Ca1 (8-fold coordinated), and Ca2 (6-fold coordinated). A (=Ca3) is occupied by Pb2+ (or Ba2+) in 6+4 coordination, or 6+1 when occupied by Ca; this third site occurs within the 3R-layer in a peripheral position. Three minerals belong to this group: margarosanite (ideally PbCa2Si3O9), walstromite (BaCa2Si3O9) and breyite (CaCa2Si3O9). So far, no solid solutions involving the Ca1 and Ca2 sites have been described. Therefore, root names depend on the composition of the Ca3 site only. Isomorphic replacement at the Ca3 sites has been noted. We here report data on a skarn sample from the Jakobsberg Mn-Fe oxide deposit, in Värmland, Sweden, representing intermediate compositions on the walstromite-margarosanite binary, in the range ca. 50-70% mol.% BaCa2Si3O9. The Pb-rich walstromite is associated closely with celsian, phlogopite, andradite, vesuvianite, diopside and nasonite. A crystal-structure refinement (R1 = 4.8%) confirmed the structure type, and showed that the Ca3 (Ba, Pb) site is split into two positions separated by 0.39 A, with the Ba atoms found slightly more peripheral to the 3R-layers

Revisiting the fall of the Veramin meteorite

The Veramin meteorite, believed to have fallen in 1880, near Varamin, Tehran province, Iran (then Persia), is one of few witnessed falls of a mesosiderite, a rare type of stony-iron meteorite. In this review, it is described that historical records show inconsistencies regarding the fall, and consequently, the naming of the meteorite. The earliest printed account, by Ferdinand Dietzsch in 1881, reported that the meteorite fell near the village “Karand” east of Tehran, with a thunder-like sound. The Shah had ordered an examination of it. Later, meteoricist Aristides Brezina named it “Veramin”. Further historical accounts include descriptions by Iranian official Mohammad Hassan Khan Sani' od-Dowlah and the explorer Sven Hedin. A key document is a Persian text on a cardboard, preserved with the main meteorite mass in Tehran's Golestan Palace. Members of the nomadic Shahsevan-e Baghdadi tribal confederacy, who had winter settlements west of Tehran, are reported as eyewitnesses. The geologist Henry A. Ward provided a detailed description in 1901, confirming the meteorite's composition and securing a larger mass for analysis and distribution to museums. The exact location and date of the fall remain uncertain due to imprecise and conflicting sources. The most likely impact field is the Booghin-Eshtehard area west of Tehran, with the event happening sometime in the period February to April 1880. The original mentioning of “Karand” is a confusion with Zarand(ieh), 70 km to the west of Varamin.</p

Description and recognition of potassic-richterite, an amphibole supergroup mineral from the Pajsberg ore field, V&#228;rmland, Sweden

Potassic-richterite, ideallyAKB(NaCa)CMg5TSi8O22W(OH)2, is recognized as a valid member of the amphibole supergroup (IMA-CNMNC 2017\u2013102). Type material is from the Pajsberg Mn-Fe ore field, Filipstad, V\ue4rmland, Sweden, where the mineral occurs in a Mn-rich skarn, closely associated with mainly phlogopite, jacobsite and tephroite. The megascopic colour is straw yellow to grayish brown and the luster vitreous. The nearly anhedral crystals, up to 4\ua0mm in length, are pale yellow (non-pleochroic) in thin section and optically biaxial ( 12), with \u3b1 = 1.615(5), \u3b2 = 1.625(5), \u3b3 = 1.635(5). The calculated density is 3.07\ua0g\ub7cm 121. VHN100is in the range 610\u2013946. Cleavage is perfect along 110. EPMA analysis in combination with M\uf6ssbauer and infrared spectroscopy yields the empirical formula (K0.61Na0.30Pb0.02) 110.93(Na1.14Ca0.79Mn0.07) 112(Mg4.31Mn0.47Fe3+0.20) 115(Si7.95Al0.04Fe3+0.01) 118O22(OH1.82F0.18) 112for a fragment used for collection of single-crystal X-ray diffraction data. The infra-red spectra show absorption bands at 3672\ua0cm 121and 3736\ua0cm 121for the \u3b1 direction. The crystal structure was refined in space group C2/m to R1 = 3.6% [I\ua0> 2\u3c3(I)], with resulting cell parameters a = 9.9977(3) \uc5, b = 18.0409(4) \uc5, c = 5.2794(2) \uc5, \u3b3 = 104.465(4)\ub0, V = 922.05(5) \uc53and Z = 2. The A and M(4) sites split into A(m) (K+), A(2/m) (Na+), A(2) (Pb2+), and M(4\u2032) (Mn2+) subsites, respectively. The remaining Mn2+is strongly ordered at the octahedrally coordinated M(2) site, possibly together with most of Fe3+. The skarn bearing potassic-richterite formed at peak metamorphism, under conditions of low SiO2and Al2O3activities and relatively high oxygen fugacities

The Rare Earth Elements: demand, global resources, and challenges for resourcing future generations

The rare earth elements (REE) have attracted much attention in recent years, being viewed as critical metals because of China’s domination of their supply chain. This is despite the fact that REE enrichments are known to exist in a wide range of settings, and have been the subject of much recent exploration. Although the REE are often referred to as a single group, in practice each individual element has a specific set of end-uses, and so demand varies between them. Future demand growth to 2026 is likely to be mainly linked to the use of NdFeB magnets, particularly in hybrid and electric vehicles and wind turbines, and in erbium-doped glass fiber for communications. Supply of lanthanum and cerium is forecast to exceed demand. There are several different types of natural (primary) REE resources, including those formed by high-temperature geological processes (carbonatites, alkaline rocks, vein and skarn deposits) and those formed by low-temperature processes (placers, laterites, bauxites and ion-adsorption clays). In this paper, we consider the balance of the individual REE in each deposit type and how that matches demand, and look at some of the issues associated with developing these deposits. This assessment and overview indicate that while each type of REE deposit has different advantages and disadvantages, light rare earth-enriched ion adsorption types appear to have the best match to future REE needs. Production of REE as by-products from, for example, bauxite or phosphate, is potentially the most rapid way to produce additional REE. There are still significant technical and economic challenges to be overcome to create substantial REE supply chains outside China

Barysilite from Garpenberg Norra, Dalarna, Sweden: occurrence and crystal structure refinement

AbstractA new occurrence of barysilite, Pb8Mn(Si2O7)3, at the polymetallic Garpenberg Norra Zn-Pb deposit, Hedemora, Dalarna, Sweden, is described. The mineral, which forms colourless, transparent grains, is characterized by X-ray diffraction and electron-microprobe analyses. The assemblage includes tephroite, zincian jacobsite, manganoan diopside and others. The crystal structure of a barysilite crystal from Garpenberg Norra was redetermined using single-crystal X-ray diffraction data (Mo-Kα, CCD area detector) and has been refined in space group Rc with a = 9.804(1), c = 38.416(8)Å, V = 3197.8(8)Å3, to R1 = 2.32% for 1025 ‘observed’ reflections with Fo &gt;4σ(Fo). A previous, low-precision structure determination (Lajzérowicz, 1965; R = 20%) is confirmed but improved considerably. The structure contains one distorted MnO6 polyhedron with six equivalent Mn–O bonds (2.224 Å), one Si2O7 disilicate unit with an Si–O–Si angle of 120.9°, and two non-equivalent Pb sites. The Pb1 site has a highly irregular, one-sided coordination with six O ligands, indicating a stereoactive 6s2 lone-electron pair on the Pb2+ ion, whereas the [6+3]-coordinated Pb2 site is fairly regular, with Pb–O distances of 2.540 (3×), 2.674 (3×) and 3.098 (3×) Å. The Pb2 site contains ~10% of Ca (+Ba) replacing Pb, corresponding to the structural formula Pb16(Pb,Ca)22Mn(Si2O7)3. This is the first direct proof that not only the M site in barysilite-type Pb8M(Si2O7)3 compounds can be replaced by divalent cations.</jats:p

Parageneses and compositional variations of Sb oxyminerals from Langban-type deposits in Varmland, Sweden

The L (a) over circle ngban, Nordmark and Jakobsberg Mn-Fe deposits contain the only known occurrences of filipstadite and manganostibite (ideal formulae (Mn, Mg)(2)(Sb0.55+Fe0.53+)O-4 and Mn72+SbAsO12, respectively). Filipstadite from Nordmark is newly r</p

Molybdophyllite: crystal chemistry, crystal structure, OD character and modular relationships with britvinite

AbstractA detailed crystal-chemical study of the complex layered silicate molybdophyllite was conducted using single-crystal X-ray diffraction (XRD) methods, supplemented by powder XRD, infrared (IR) and Raman spectroscopic studies, chemical analyses by energy-dispersive spectrometry (EDS) on a scanning electron microscope (SEM), and electron probe microanalysis (EPMA). The results, based on several samples from both Långban and Harstigen, Filipstad, Sweden, show that the crystal structure of molybdophyllite has an order-disorder (OD) character. The latter is especially evident in specimens from Långban which display a complex diffraction pattern characterized by the simultaneous presence of sharp spots, diffuse reflections and continuous streaks. The sharp reflections define the unit cell of the family structure (a = 3.124, c = 41.832 Å, space group R32). Two main polytypes (maximum degree of order structures) are indicated by the OD approach: a trigonal one and a monoclinic one; the latter polytype is the most common in the samples that were studied and has space group C2, with a = 16.232(6), b = 9.373(2), c = 14.060(3) Å, b = 97.36(4)º and V = 2121.5(10) Å3.The crystal structure determination [R1 = 0.096], together with the EPMA, IR and Raman data, reveal that molybdophyllite is built up by a regular alternation of complex layers with a composition {Mg9[Si10O28(OH)8][OPb4]2}6+ and simple layers with a composition [(CO3)3·H2O]6–, leading to the ideal crystal-chemical formula Pb8Mg9[Si10O28(OH)8|O2|(CO3)3]·H2O (Z = 2).This contribution is mainly devoted to the results obtained for molybdophyllite sensu stricto, but new data for britvinite [i.e. 'molybdophyllite-18 Å'] are also presented and its modular relationship with molybdophyllite is discussed.</jats:p