Beryl Crystals Research Articles

Нано- и микроморфологические доказательства коллоидной структуры содержимого включений кольцевых силикатных кристаллов

The substance released naturally during mechanical opening of growth inclusions of aquamarine, beryl and tourmaline crystals (Transbaikalia, Russia) has been studied by scanning atomic force microscopy (AFM) and electron microscopy (SEM). The liquid part of the substance of the inclusions is a sufficiently concentrated colloidal sol-gel-silicate system. The diffused silicate colloid forms a film, poorly removable from the chip surface, which is reliably detected by AFM and transformed under prolonged exposure to an electron beam into a foam-glass. The latter fact can be used to create sub-micron textures that are stable under normal conditions by electron-beam lithography. The study of quartz and phenacite (Ural, Russia) did not reveal such films. In contrast to aquamarine, the inner walls of cavities of quartz and phenacite inclusions, according to AFM data, are covered with growth hills, grown by the dislocation mechanism. This indicates a relatively low degree of polymerization of the silicate component in the initial hydrothermal mother liquor for quartz and phenacite compared to the degree of polymerization in the mineral-forming media of ring silicate crystals.

Li-Be-Nb-Ta mineralogy of the Kuqu leucogranite and pegmatite in the Eastern Himalaya, Tibet, and its implication

稀有金属矿物记录了花岗伟晶岩成岩成矿的重要信息。喜马拉雅是全球著名的淡色花岗岩带，库曲岩体位于喜马拉雅东段的特提斯喜马拉雅岩系中。本文调查了库曲岩体的二云母花岗岩、白云母花岗岩、电气石花岗岩和花岗伟晶岩，其中，花岗伟晶岩涉及花岗岩的伟晶岩相和独立伟晶岩脉。库曲岩体产出的稀有金属矿物包括锂辉石、锂绿泥石、绿柱石、铌铁矿-钽铁矿、钇铀钽烧绿石和细晶石，它们主要赋存于似文象伟晶岩、石英-钠长石-白云母伟晶岩、块体长石-钠质细晶岩、块体长石-电气石钠质细晶岩、锂辉石-块体长石-细晶岩、白云母花岗岩的伟晶岩相以及电气石花岗岩内。显微镜观察、电子探针和LA-ICP-MS测试结果显示锂辉石具有四种产状，包括粗粒锂辉石自形-半自形晶、细粒锂辉石-石英镶嵌晶、中细粒锂辉石-钾长石-钠长石-云母镶嵌晶以及发育锂绿泥石的粗粒锂辉石，揭示了其形成时复杂的熔流体动荡结晶环境。绿柱石背散射电子图像（BSE）下呈均一结构和不均一结构（蚀变边、不规则分带和补丁分带），元素替代机制包括通道-八面体替代、通道-四面体替代以及通道中碱金属阳离子间的置换。铌铁矿族矿物包括原生、蚀变边和不规则分带结构，部分被钇铀钽烧绿石和细晶石交代。与原生铌铁矿相比，蚀变边和不规则分带铌铁矿族矿物总体上富钽贫锰，显示了结晶分异、过冷却引起的过饱和以及流体作用。根据稀有金属矿物揭示的成因信息，独立伟晶岩脉（似文象伟晶岩）、白云母花岗岩的伟晶岩相和电气石花岗岩在岩浆分异程度、经历的演化过程、以及流体活动方面存在差异，很可能是不同期次岩浆活动的产物。库曲岩体绿柱石的Rb和Zn含量、以及铌铁矿族矿物的Sc₂O₃、SiO₂和PbO含量，与已有指示标志存在相关性，作为潜在指示标志仍需开展更多的研究工作。综合含锂辉石伟晶岩的产出、岩浆分异演化程度、多期花岗质岩浆活动、复杂的流体作用以及所属锂丰度高值区等因素，库曲岩体是喜马拉雅东段找锂的有利地段。;The rare-element minerals record important information of rock-forming process and metallogenesis. Himalaya is a famous leucogranite belt. The Kuqu intrusion is located in the Tethys Himalayan sedimentary sequence in the Eastern Himalaya. This study investigated two-mica granite, muscovite granite, tourmaline granite and granitic pegmatites in the Kuqu intrusion. The granitic pegmatites refer to either the pegmatite rocks that are included in and related to granite or the pegmatite zones that make up a single pegmatite dyke. The rare-element minerals identified in the Kuqu intrusion include spodumene, cookeite, beryl, columbite-tantalite, Y-hatchettolite and microlite. They are distributed in quartz-feldspar-muscovite pegmatite, quartz-albite-muscovite pegmatite, blocky feldspar-aplite, block feldspar-tourmaline aplite, spodumene-blocky feldspar-aplite, pegmatite rock in muscovite granite, and tourmaline granite. The EMPA and LA-ICP-MS analytical results indicate that spodumenes show four occurrences which consists of coarse-grained subhedral to euhedral spodumene, fine-grained symplectitic reaction border composed of spodumene and quartz, middle to fine-grained mosaic structure of spodumene, K-feldspar, albite and muscovite, and coarse-grained spodumene filled by cookeite veins. These occurrences of spodumene reveal a complex and fluid-rich unstable crystallization environment. There are homogeneous and heterogeneous beryl crystals in the intrusion. The internal zonation patterns for heterogeneous beryls are alteration border, patches and complex irregular zoning in BSE images. The substitution mechanisms of beryl in the Kuqu intrusion are channel-octahedral, channel-tetrahedral and alkali cations in channel. The columbite-group mineral crystals are composed of primary part and alteration border or display irregular zoning pattern, some of which are altered by Y-hatchettolite and microlite. Compared with primary parts, the alteration border and irregular zoned crystals have higher Ta/(Nb+Ta) values and lower Mn/(Fe+Mn) values, indicating fractional crystallization, supersaturation caused by strong undercooling, and fluid activities. Based on the studies of rare-element minerals, the single pegmatite dyke (quartz-feldspar-muscovite pegmatite), pegmatite rock in muscovite granite and tourmaline granite display differences on the degree of fractionation of magma, evolution processes and fluid activities and they might be magma products of different stages. The Rb and Zn contents of beryl, and Sc₂O₃, SiO₂ and PbO contents of columbite-group minerals show correlation with the existed indicators for evolution degree of magma, but more studies are needed to carry out for them to be possible indicators. Considering the spodumene-bearing pegmatite indentified in the intrusion, the high degree of magma evolution, multistage of magmatism, complex fluid activities and being in a high lithium abundance value area, the Kuqu intrusion is an important potential area for future lithium prospecting in the Eastern Himalaya.

Historiography and FTIR spectral signatures of beryl crystals from some ancient Roman sites in the Eastern Desert of Egypt

Beryl (mostly emerald) was mined in Egypt since Antiquity, particularly the so-called “Cleopatra’s Mines” in the Eastern Desert were a major source of emerald in the world during the Roman era in northeast Africa. Emerald from the Nugrus belt is located at Sikait, Um Sleimat, Um Addebbaa and Um Kabu areas where the ancient mines are confined structurally and genetically to “schist-type” deposits as a part of the Neoproterozoic ophiolitic melange. At Homret Mikpid and Homr Akarem occurrences, non-gem beryl occurs in greisinized granites, pegmatites and quartz veins. Fourier transform infrared (FTIR) spectroscopy is able to distinguish Egyptian emeralds from non-gem beryls. Different types of H2O molecules and OH-groups can be identified in all especially at ~ 3435–3480 cm−1 as an indication of X-site occupancy of Na and vacancy (□) and to the Y-site M2+ and M3+ cation distribution. High wavenumber bands > 3600 cm−1, e.g. at ~ 3865–3988 cm−1 are characteristics of non-gem beryl only. Structural CO2 molecules are seen in both emerald and beryl at ~ 2360 cm−1. About 97–99% (at a wavelength range of 335–611 nm.) infrared reflectance of non-gem beryl is much higher (97–99%) whereas it never exceeds ~ 88% (at ~ 360 nm) in emerald.

Late-stage fluid exsolution and fluid phase separation processes in granitic pegmatites: Insights from fluid inclusion studies of the Luumäki gem beryl pegmatite (SE Finland)

The fluid inclusion record of the miarolitic gem beryl-bearing Luumäki pegmatite (SE Finland) has been studied by petrography, microthermometry and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Four types of fluid inclusion assemblages could be distinguished, which record the nature and timing of fluids exsolved in the pegmatite. Type I and type II fluid inclusions are two-phase (LV) aqueous with intermediate salinities of 8.0 ± 2.7 and 8.1 ± 0.9 wt% NaCl, respectively. Type I fluids occur at the transition between the quartz core and euhedral smoky quartz crystals formed in miarolitic cavities. Type II inclusions are present throughout smoky quartz and gem beryl crystals in miarolitic cavities. Type III are three-phase (LLV), low-salinity (1.2 ± 1.1 wt% NaCl), aqueous‑carbonic inclusions, whereas type IV are three-phase (LVS) aqueous inclusions with halite daughter crystals and high salinity (39.6 ± 4.5 wt% NaCl equiv.). Both type III and type IV inclusions occur texturally late in the smoky quartz crystals and are closely related to each other, sometimes coexisting on the same inclusion trail. The chemical data show that type I, type III and type IV inclusions lie on linear trends in many elemental variation diagrams, where type I inclusions plot between the data for type III and type IV inclusions. The saline type IV inclusions are strongly enriched in many elements, such as alkalis, alkaline earths and transition metals, whereas the aqueous‑carbonic type III inclusions are depleted in these metals. The chemical data, in conjunction with petrographic features, demonstrate that type III and type IV inclusions were formed by phase separation of the type I intermediate-salinity fluid. The metal and halogen content of all four fluid types suggests that they are of magmatic-hydrothermal origin and supports the model that the Luumäki pegmatite reached fluid saturation at the transition between core quartz crystallization and formation of miarolitic cavities. Representative fluid inclusion isochores calculated for type II fluids preserved in gem beryl, in conjunction with the P-T slope constructed from the water content in beryl, yield a best P-T estimate for pocket formation of 380 ± 80 °C and 1.2 ± 0.7 kbar. This P-T estimate constrains the range of pressure-depth conditions proposed for the rapakivi granites that host the Luumäki pegmatite, and is consistent with recent estimates suggesting a maximum pressure of emplacement of 1.9 kbar.

Tourmaline as a Recorder of Ore-Forming Processes in the Xuebaoding W-Sn-Be Deposit, Sichuan Province, China: Evidence from the Chemical Composition of Tourmaline

The Xuebaoding W-Sn-Be deposit located in the Songpan-Ganze Orogenic Belt (Sichuan Province, China) is a hydrothermal deposit with less developed pegmatite stage. The deposit is famous for the coarse-grained crystals of beryl, scheelite, cassiterite, apatite, fluorite, muscovite, and others. The orebody is spatially associated with the Pankou and Pukouling granites hosted in Triassic marbles and schists. The highly fractionated granites are peraluminous, Li-Rb-Cs-rich, and related to W-Sn-Be mineralization. The mineralization can chiefly be classified based on the wallrock and mineral assemblages as muscovite and beryl in granite (Zone I), then beryl, cassiterite and muscovite at the transition from granite to triassic strata (Zone II), and the main mineralized veins composed of an assemblage of beryl, cassiterite, scheelite, fluorite, and apatite hosted in metasedimentary rock units of marble and schist (Zone III). Due to the stability of tourmaline over a wide range of temperature and pressure conditions, its compositional variability can reflect the evolution of the ore-forming fluids. Tourmaline is an important gangue mineral in the Xuebaoding deposit and occurs in the late-magmatic to early-hydrothermal stage, and can thus be used as a proxy for the fluid evolution. Three types of tourmalines can be distinguished: tourmaline disseminations within the granite (type I), tourmaline clusters at the margin of the granite (type II), and tourmalines occurring in the mineralized veins (type III). Based on their chemical composition, both type I and II tourmalines belong to the alkali group and to the dravite-schorl solid solution. Type III tourmaline which is higher in X-site vacancy corresponds to foitite and schorl. It is proposed that the weakly zoned type I tourmalines result from an immiscible boron-rich aqueous fluid in the latest stage of granite crystallization, that the type II tourmalines showing skeletal texture directly formed from the undercooled melts, and that type III tourmalines occurring in the mineralized veins formed directly from the magmatic hydrothermal fluids. Both type I and type II tourmalines show similar compositional variations reflecting the highly fractionated Pankou and Pukouling granites. The higher Ca, Mg, and Fe contents of type III tourmaline are buffered by the composition of the metasedimentary host rocks. The decreasing Na content (<0.8 atoms per formula unit (apfu)) and increasing Fe3+/Fe2+ ratios of all tourmaline samples suggest that they precipitated from oxidized, low-salinity fluids. The decreasing trend of Al content from type I (5.60–6.36 apfu) and type II (6.01–6.43 apfu) to type III (5.58–5.87 apfu) tourmalines, and associated decrease in Na, may be caused by the crystallization of albite and muscovite. The combined petrographic, mineralogical, and chemical characteristics of the three types of tourmalines thus reflect the late-magmatic to early-hydrothermal evolution of the ore-forming fluids, and could be used as a geochemical fingerprint for prospecting W-Sn-Be mineralization in the Xuebaoding district.

Comments on Beryl Colors and on Other Observations Regarding Iron-containing Beryls

Abstract Trivalent iron ions substituting for Al3+ are present in many beryls and are abundant in dark red and dark blue beryl. These ions do not contribute any color to the crystals. Dark blue beryl also contains octahedral Fe2+ ions, which are involved in giving the crystal the blue color. The colors of dark red and dark blue beryls are very stable. Tetrahedral iron ions are practically absent in these beryls, but are present in other beryls which change their color upon irradiation and heating. Their colors depend more on the radiation and temperature history of the crystals than on chemistry. Trivalent iron ions substituting for Si4+ also do not contribute color. Rare observations by EPR (electron paramagnetic resonance) indicate that the charge difference can be compensated either by protons or by alkali ions in the beryl channels. It is shown that about 1% of the Fe3+ ions in dark red beryl substitute for Si4+. The changing colors of iron-containing beryls have been interpreted in many different ways, but it is likely that they are due to ions substituting for Be2+. The present study suggests that the iron ions do not substitute isomorphically for Be, but that they enter a distorted tetrahedron which consists of one O(1) oxygen and three O(2) oxygens. The center of this T(3) tetrahedron is at (0.432, 0.344, 0.167) in the beryl structure and the distance to the four oxygen ions is 1.84 Å, compared to 1.65 Å in the Be tetrahedron, thus providing more space for the much larger iron ions. This site is so close to the Be site that both sites cannot be simultaneously occupied. Beryl crystals with Fe2+ ions in T(3) are colorless. Irradiation oxidizes these Fe2+ ions to Fe3+, which gives the beryl a yellow color. The aquamarine color is caused by pairs of Fe2+ and Fe3+ ions in neighboring T(3) tetrahedra. When both configurations are present, the crystal assumes a shade of green, depending on their relative proportion. The electrons released by the irradiation are trapped at sites which are probably associated with water molecules in the beryl channels. These electrons leave the traps upon heating and reduce the Fe3+ ions in the T(3) tetrahedra. The yellow color vanishes and the beryl becomes aquamarine blue. More electrons are released at higher temperatures and reduce both ions of the pairs, leaving the beryl colorless. The oxidation of the iron ions at even higher temperatures is connected with the release of water from the beryl crystal. A number of small EPR signals in addition to the large signal from octahedral Fe3+ ions in iron-containing beryl crystals are investigated. Many arise from exchanged-coupled Fe3+ ion pairs, and one is related to the yellow color.

Formation Conditions and 40Ar/39Ar Age of the Gem-Bearing Boqueirão Granitic Pegmatite, Parelhas, Rio Grande do Norte, Brazil

The Boqueirão granitic pegmatite, alias Alto da Cabeça pegmatite, is situated in Borborema Pegmatitic Province (BPP) in Northeast Brazil. This pegmatitic province hosts globally important reserves of tantalum and beryllium, as well as significant quantities of gemstones, including aquamarine, morganite, and the high-quality turquoise-blue “Paraíba Elbaite”. The studied lithium-cesium-tantalum Boqueirão granitic pegmatite intruded meta-conglomerates of the Equador Formation during the late Cambrian (502.1 ± 5.8 Ma; 40Ar/39Ar plateau age of muscovite). The pegmatite exhibits a typical zonal mineral pattern with four defined zones (Zone I: muscovite, tourmaline, albite, and quartz; Zone II: K-feldspar (microcline), quartz, and albite; Zone III: perthite crystals (blocky feldspar zone); Zone IV: massive quartz). Huge individual beryl, spodumene, tantalite, and cassiterite crystals are common as well. Microscopic examinations revealed that melt inclusions were entrapped simultaneously with fluid inclusions, suggesting the magmatic–hydrothermal transition. The magmatic–hydrothermal transition affected the evolution of the pegmatite, segregating volatile compounds (H2O, CO2, N2) and elements that preferentially partition into a fluid phase from the viscous silicate melt. Fluid inclusion studies on microcline and associated quartz combined with microthermometry and Raman spectroscopy gave an insight into the P-T-X characteristics of entrapped fluids. The presence of spodumene without other LiAl(SiO3)2 polymorphs and constructed fluid inclusion isochores limited the magmatic–hydrothermal transition at the gem-bearing Boqueirão granitic pegmatite to the temperature range between 300 and 415 °C at a pressure from 1.8 to 3 kbar.

Development of sigmoidal en-échelon microfractures in beryl and the role of strain localization evidenced by fluid inclusions

A combined fluid inclusion and microstructural study was carried out in beryl crystals from the San Cayetano Nb-Ta-bearing pegmatite (San Luis, Argentina). Primary aqueous-carbonic fluids (T0) were subsequently re-trapped during shearing, resulting in en-échelon microfractures. The more brittle behaviour of beryl compared to quartz makes this mineral more suitable for the preservation of fluid inclusions and microstructures. The primary inclusions T0 are preserved in strain-free domains, whereas the pseudo-secondary T1-to T3-type inclusions occur in domains showing intracrystalline deformation. CO2 was relatively immobile or reacted to form carbonate in early T1-type inclusions, whereas H2O preferentially migrated along microfractures and was trapped as T2-and T3-type inclusions. Short intragranular trails of fluid inclusions, representing en-échelon healed microfractures, resulted from progressive strain localization. Contrary to previous proposals, this new model implies the progressive thickness reduction of intracrystalline micro-shear zones. Besides, hydrolytic weakening linked to dislocation glide is the most likely mechanism to explain the evolution of fluid inclusions, with intracrystalline deformation enhancing anisotropic diffusion. This study highlights the potential of combined fluid inclusion and microstructural studies in order to understand the interaction between fluid activity and deformation. In this way, valuable insights can be provided into the progressive development of overprinted fabrics and low-to medium-temperature deformation mechanisms of minerals.

A NEW INVESTIGATION OF VIETNAM’S BERYL

The paper presents briefly new investigation of Vietnam beryl group, especially some characteristics of regional geology of Song Chay granite massif and new find of big crystals of beryl in them. The green beryl is found in quartz - mica - tourmaline, mica - feldspar – quartz pegmatite bodies in the south part of Song Chay granite - gneiss massif near Na Chi and Tan Nam villages, Quang Binh district, Ha Giang province.

Applying Semi-Empirical Quantum Harmonic Calculations for Studying the Atomic Kinetic Energies in Hydrogen Bonded Systems

The use of the semi empirical (SE) quantum harmonic approach for calculating the proton’s mean kinetic energy, Ke(H), of systems containing hydrogen bonds (HB), is reviewed. The value of Ke(H) provides very interesting information on the proton dynamics, anharmonicity, and quantum effects. This method uses the IR/Raman and inelastic neutron scattering frequencies of the system as input data and assumes the harmonic approximation. The systems studied encompass a wide range of HBs strengths, from weak occurring in e.g. pure H2O phases and Silanol groups, via moderate, as in ferro-electric KDP-type crystals, to strong ones as in highly compressed ice VII and the superprotonic Rb3H(SO4)2 conductor. The comparison of SE results with electron (ECS) and neutron (NCS) Compton scattering measurements revealed many cases of very good agreements. In recent years, however, unusual Ke(H) values, using NCS, were reported in confined water within ≤ 20 Å size cavities such as in carbon nanotubes (CNTs) and in Beryl crystal. The Ke(H) values were found to depart strongly from those of the non-confined water. In an attempt to understand those anomalies, SE study was carried out, focusing on nano-confined samples meeting the ≤ 20Å size criteria, including carbon nanotubes, Beryl and Bikitaite. These calculations failed to reproduce the NCS anomalies. Possible sources for the discrepancies were discussed and further research to reconcile this open question was proposed. Keywords: Harmonic approximation, hydrogen bonds, kinetic energy, libration, nano-confinement, neutron scattering, proton, vibrational density of states.

Submillimeter ESR spectra of Fe2+ ions in synthetic and natural beryl crystals

Electron spin resonance spectra of non-Kramers bivalent iron (Fe2+) ions have been detected in synthetic and natural beryl crystals with an iron impurity. The observed ESR spectra have been attributed to resonance transitions of Fe2+ ions from the ground (singlet) state to excited (doublet) levels with the splitting Δ = 12.7 cm–1 between the levels. The experimental angular and frequency dependences of the resonance field of the ESR signal have been described by the spin Hamiltonian with the effective spin S = 1. The analysis of the ESR data and optical absorption spectra indicates that the Fe2+ ions are situated in tetrahedral positions and substitute Be2+ cations in the beryl structure.

Infrared Spectroscopic Characteristics and Ionic Occupations in Crystalline Tunneling System of Yellow Beryl

Infrared spectroscopic characteristics and ionic occupations in a crystalline tunneling system of yellow beryl crystals from Inner Mongolia, China, were investigated by standard gemological methods, laser ablation inductively coupled plasma mass spectrometry, x-ray diffraction, ultraviolet–visible (UV–Vis) spectrophotometry, and infrared (IR) spectroscopy in this study. The refractive index, specific gravity, and chemical composition of the samples are shown within the range of natural yellow beryls previously reported. The unit cell dimensions of the beryls are 9.208–9.212 A for a and 9.105–9.206 A for c with a ratio of c/a = 0.9985–0.9994. The beryl samples are generally alkali-poor beryls with Fe <0.05 and alkali <0.03 atoms per formula unit in the channel sites. The standard gemological test and mid-IR confirmed that these samples are natural beryl. However, polarized UV–Vis spectra showed an absorption band at 689 nm, and all polarized IR spectra of samples displayed a 7217-cm−1 infrared absorption in the studied samples which was associated with irradiation of the coloration. This treatment of color irradiation can be detected from the beryl channels with 689-nm absorption and 7217-cm−1 infrared absorption.

Atomic resolution imaging of beryl: an investigation of the nano-channel occupation.

Beryl in different varieties (emerald, aquamarine, heliodor etc.) displays a wide range of colours that have fascinated humans throughout history. Beryl is a hexagonal cyclo-silicate (ring-silicate) with channels going through the crystal along the c-axis. The channels are about 0.5 nm in diameter and can be occupied by water and alkali ions. Pure beryl (Be3 Al2 Si6 O18 ) is colourless (variety goshenite). The characteristic colours are believed to be mainly generated through substitutions with metal atoms in the lattice. Which atoms that are substituted is still debated it has been proposed that metal ions may also be enclosed in the channels and that this can also contribute to the crystal colouring. So far spectroscopy studies have not been able to fully answer this. Here we present the first experiments using atomic resolution scanning transmission electron microscope imaging (STEM) to investigate the channel occupation in beryl. We present images of a natural beryl crystal (variety heliodor) from the Bin Thuan Province in Vietnam. The channel occupation can be visualized. Based on the image contrast in combination with ex situ element analysis we suggest that some or all of the atoms that are visible in the channels are Fe ions.

The Rietveld Refinement of Beryls from Pegmatitic System at Piława Górna, Góry Sowie Block, SW Poland

The studied beryl crystals came from the Julianna pegmatitic system exposed in the Dolno-liskie Surowce Skalne S.A. quarry at Piawa Gorna. This mineral occurs here in various forms and colours (green, yellow, white, pinkish and blue) in almost all pegmatite bodies. The paper describes the relationship between the structure and chemical composition of dierent coloured beryl crystals.

Local compressibilities of Cr3+ octahedral clusters in the natural and synthetic emerald crystals

The local linear compressibilities of Cr3+ octahedral clusters in the natural and synthetic emerald (Be3Al2Si6O18: Cr3+) crystals are investigated by analyzing their pressure-induced R-line shifts. The results show that the local compressibility of Cr3+ cluster in the synthetic emerald is slightly smaller than that in the natural emerald, suggesting that the atom arrangement of Cr3+ impurity clusters in the synthetic emerald is slightly tighter than that in the natural one. The point is supported by the observed cubic field parameters Dq in the two emerald crystals. The local compressibilities of Cr3+ clusters in both the natural and synthetic emeralds are also slightly different from that of the whole host beryl (Be3Al2Si6O18) crystal. The causes are discussed.

Non-pegmatitic beryl related to Carboniferous granitic magmatism, Velasco Range, Pampean Province, NW Argentina

The specialized leuco-monzogranite of the La Chinchilla Stock is a small Carboniferous stock located in the center of the Velasco Range, Pampean Province, La Rioja, Argentina. It is highly evolved and locally F- and Be-bearing, and has the potential for hosting U mineralization. Three different facies can be identified in the granitoid: border, porphyritic and equigranular facies. In all three facies the main minerals are quartz, microcline, plagioclase, biotite, and muscovite. Accessory minerals present in all facies include fluorite, zircon, and apatite. In addition, monazite, rutile, and uraninite occur as accessory minerals in the equigranular facies. Secondary minerals are muscovite, sericite, kaolinite, and opaque minerals. Secondary uranophane occurs in the equigranular and border facies. In localized areas, the equigranular facies contains small, green idiomorphic crystals of beryl (Be3Al2Si6O18) as accessory mineral. One of these beryl crystals was chemically analyzed for major and minor element contents using an electron microprobe and this information, along with fractional crystallization models and comparison with compositions of non-pegmatitic beryl from the literature, were used to understand the degree of evolution of the granitic melt. The chemical formula of beryl from the La Chinchilla Stock can be written as: C(Na0.014-0.033, K0.001-0.002, Ca0.001-0.004) T(2)(Be2.978-2.987, Li0.016-0.022) O(Al1.889-1.967, Fe0.045-0.103, Mg0.001-0.007, Mn0.001-0.007) T(1)(Si5.994-6.040O18). The alkali contents are low (Na2O&lt;0.18 wt%; K2O&lt;0.02 wt%), while FeOt is dominant among the divalent cations that substitute trivalent aluminum in the octahedral position of the mineral (FeOt/(MgO+MnO)&gt;6; FeOt&lt;1.27 wt%). In a longitudinal geochemical profile, Al enrichment is observed at the border while the highest Na content is found in an internal point. In a transversal geochemical profile, the highest concentration of Al is seen in an internal point while Na remains almost invariable. Ferromagnesian elements vary randomly within the crystal. This indicates compositional changes in the magma for Al, ferromagnesian elements, and Na. The FeOt content of the analyzed beryl is within the compositional range of other disseminated beryl from granitoids but slightly higher than that of beryl from hydrothermal veins and greisens. It contains similar to slightly lower amounts of FeOt, MgO, and Na2O than beryl from medium to little evolved granitic pegmatites. Overall, the composition of beryl in the La Chinchilla Stock is quite similar to that from medium to poorly evolved granitic pegmatites of the nearby Velasco Pegmatite District. The formation of beryl in the La Chinchilla Stock is attributed to precipitation from a F-bearing, highly fractionated, Al- and Si-rich melt saturated in BeO. A fractional crystallization model using Rb and Ba suggests that the beryl-hosting rock crystallized from the parent melt after extreme fractionation and 75% crystallization. The occurrence of beryl as a magmatic accessory mineral in the equigranular facies of the La Chinchilla Stock is indicative of a very high degree of fractionation of the parental magma.

Optical Properties of Natural and Synthetic Minerals

The results of investigation of optical absorption and photoluminescence (PL) of topaz, beryl and yttrium aluminium garnet crystals doped with different concentrations of transition ions exposed to fast neutron irradiation and electron irradiation are presented. We suppose that irradiation leads to the formation of two types of complex centers: "Me2+-F+ (or F) centre" and complex centers, which consist of a cation vacancy and an impurity (iron, manganese and chromium) ion. Exchange interaction between radiation defects and impurity ions during neutron or electron irradiation gives rise to appearance of additional absorption and luminescence band broadening in investigated crystals.

X‐Ray micro‐Computed Tomography and micro X‐ray Fluorescence mapping of synthetic emerald by using a laboratory polycapillary optics X‐ray tube layout

This paper relates the X‐ray micro‐Computed Tomography and micro X‐ray Fluorescence 2D mapping of a synthetic emerald performed by a conventional X‐ray source matched with polycapillary optics. The investigated crystals were synthesized in 1888 by Hautefeuille and Perrey starting from a stochiometric oxide mixture and using LiMoO4 as a flux; Cr was added to the system to give the green‐color to the resulting crystals. Preliminary scanning electron microscope‐backscattered electron images, coupled with wavelength‐dispersive spectrometry microanalyses, showed a peculiar ‘hourglass’ distribution of Cr across the beryl crystals. In this contribution, we show the capability of a laboratory polycapillary lenses/X‐ray tubes layout to characterize at the micrometric scale; the 3D spatial distribution of Cr in these emerald crystals. Actually, this technique offers many opportunities to characterize natural and technological materials where zoning of particular chemical elements occur at the micron or sub‐micron scale. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Optical Properties of Natural and Synthetic Beryl Crystals

The results of investigation of photoluminescence and UV-Visible absorption spectra of natural beryl crystals from Ural Mountains before and after fast neutron irradiation and synthetic crystal grown in Belarus and Russia are presented. Photoluminescence (PL) spectra of synthetic beryl crystals contain a broad band with maxima 740 nm excited both by UV light (λex = 260 nm, 271 nm) and laser excitation (λex =263 nm). This band is connected with Fe2+ ions. The temperature lowering down to 8 K leads to appearance of narrow lines in the 680 – 720 nm regions. Emission lines observed in the luminescence spectra are connected with electron transition 2Eg→4A2g of the Cr3+ ions: R-lines (682.5 nm) arise from isolated Cr3+ ions occupying Al3+ sites; N-lines (691, 698, 703, 706 and 711 nm) arise from several types of exchange-coupled pairs of Cr3+ ions occupying first, second and third nearest and related neighbour Al3+ sites. It is shown that the absorption bands in the 690-580 nm region of natural pale blue beryl crystals caused by neutron irradiation belong to a complex center, which consists of Cr3+ ions and radiation defect - F or F+- center. Presence of Fe2+ ions contributes to the persistence of the complex defect.

Optical and crystal-chemical changes in aquamarines and yellow beryls from Thanh Hoa province, Vietnam induced by heat treatment

Optical and crystal-chemical changes in two beryl varieties after the heat treatment were determined using a wide spectrum of analytical methods. Studied aquamarines are generally more enriched in Fe (up to 0.25 apfu) and alkali (up to 0.08 apfu) than yellow beryls (up to 0.07 apfu Fe, up to 0.04 apfu alkali). The determined c/a ratio of 0.997–0.998 classified all our studied beryls as “normal” beryls. While no crystal structure changes were observed in samples heated to 700 °C, those heated to 900 and 1,100 °C exhibited cracks and fissures. Reduced Fe occurred in samples heated between 300 and 700 °C, and subsequent oxidation from 900 to 1,100 °C induced changes in their colour and clarity. The Fe-bearing beryl colour is controlled by the position of the absorption edge and the presence of a broad band attributed to Fe2+ in the NIR region. Blue colour results from the absorption edge located deeper in the UV region and the presence of broad band in the NIR region. Shift of absorption edge to the visible region at the presence of the broad band gives a yellow colour. Although our studied beryls are enriched in H2O I molecule due to their low alkali content, the H2O II molecule is also present. The following two dehydration processes were observed: (1) release of one double-coordinating H2O II molecule at 300–500 °C and (2) total dehydration at 900–1,100 °C. The observed cracks and fissures likely resulted from channel water release in large beryl crystals.