Characterization of metamict minerals with complex crystal-chemical properties - allanite example

Rekristalizacija uzoraka allanita različitog stupnja metamiktnosti je inducirana žarenjem uzoraka na zraku, te u uvjetima inertne i reduktivne atmosfere na odabranim temperaturama. Do 800C metamiktni uzorci allanita djelomično rekristaliziraju u kristalnu strukturu allanita, no kod jače metamiktnih uzoraka već na ovoj temperaturi dolazi do pojavljivanja novih faza, cerijanita i hematita. Zbog oksidacije Fe2+ i Ce3+, te posljedično otpuštanja OHaniona, u danim uvjetima, nemoguće je ostvariti potpunu rekristalizaciju, a na višim temperaturama (> 900C) kristalna struktura allanita se u potpunosti raspada na jednostavnije okside (cerijanit, hematit), fosfate (britholit) i silikate (anortit). Iz tog razloga su odabrani uzorci hidrotermalno tretirani na nižim (150 -250C), te višim (400-800C) temperaturama na kojima dolazi do potpune rekristalizacije metamiknih uzoraka allanita, neovisno o stupnju metamiktnosti, bez pojave dodatnih faza. Jedan uzorak allanita je podvrgnut bombardiranju neutronima radi rušenja kristalne strukture, što je djelomično uspješno izvršeno. Svi procesi su praćeni difrakcijom rentgenskih zraka na prahu, visokorazlučujućom transimisijskom elektronskom mikroskopijom, te elektronskom difrakcijom, IR, Raman i Mössbauer spektroskopijom te termičkim metodama.Recrystallization of allanite with different degrees of metamictization is induced by annealing of samples in air, inert and reductive atmosphere at chosen temperatures. Up to 800C metamict samples of allanite partially recrystallize to allanite crystal structure, but with heavily metamictized samples, already at these temperatures, new phases such as cerianite and hematite, occur. It is impossible to accomplish complete recrystallization in these conditions due to oxidation of Fe2+ and Ce3+, and escape of OHanion from the structure, and at higher temperatures (> 900C), allanite crystal structure breaks down to a mixture of simple oxides (cerianite an hematite), phosphate (britholite) and silicate (anorthite). Thus, chosen samples were hydrothermally treated at lower (150 -250C), and higher (400-800C) temperatures when complete recrystallization, without additional phases and regardless of the degree of metamictization, occurs. One allanite sample was bombarded with neutron flux, in order to destroy its crystal structure, what was partially accomplished. All processes were monitored by X-ray powder diffraction, high-resolution transmission electron microscopy coupled with electron diffraction, IR, Raman and Mössbauer spectroscopy, and thermal methods

Trace Element and Sulfur Isotope Signatures of Volcanogenic Massive Sulfide (VMS) Mineralization: A Case Study from the Sunnhordland Area in SW Norway

The Sunnhordland area in SW Norway hosts more than 100 known mineral occurrences, mostly of volcanogenic massive sulfide (VMS) and orogeny Au types. The VMS mineralization is hosted by plutonic, volcanic and sedimentary lithologies of the Lower Ordovician ophiolitic complexes. This study presents new trace element and δ 34S data from VMS deposits hosted by gabbro and basalt of the Lykling Ophiolite Complex and organic-rich sediments of the Langevåg Group. The Alsvågen gabbro-hosted VMS mineralization exhibits a significant Cu content (1.2 to >10 wt.%), with chalcopyrite and cubanite being the main Cu-bearing minerals. The enrichment of pyrite in Co, Se, and Te and the high Se/As and Se/Tl ratios indicate elevated formation temperatures, while the high Se/S ratio indicates a contribution of magmatic volatiles. The δ 34S values of the sulfide phases also support a substantial influx of magmatic sulfur. Chalcopyrite from the Alsvågen VMS mineralization shows significant enrichment in Se, Ag, Zn, Cd and In, while pyrrhotite concentrates Ni and Co. The Lindøya basalt-hosted VMS mineralization consists mainly of pyrite and pyrrhotite. Pyrite is enriched in As, Mn, Pb, Sb, V, and Tl. The δ 34S values of sulfides and the Se/S ratio in pyrite suggest that sulfur was predominantly sourced from the host basalt. The Litlabø sediment-hosted VMS mineralization is also dominated by pyrite and pyrrhotite. Pyrite is enriched in As, Mn, Pb, Sb, V and Tl. The δ 34S values, which range from −19.7 to −15.7 ‰ VCDT, point to the bacterial reduction of marine sulfate as the main source of sulfur. Trace element characteristics of pyrite, especially the Tl, Sb, Se, As, Co and Ni concentrations, together with their mutual ratios, provide a solid basis for distinguishing gabbro-hosted VMS mineralization from basalt- and sediment-hosted types of VMS mineralization in the study area. The distinctive trace element features of pyrite, in conjunction with its sulfur isotope signature, have been identified as a robust tool for the discrimination of gabbro-, basalt- and sediment-hosted VMS mineralization

Morfologija kristala i rentgenografske osobitosti brazilijanita s različitih lokaliteta

Forty four brazilianite crystals from several localities in Brazil, Rwanda and Canada were measured on a two-circle goniometer to determine brazilianite morphology. Twenty forms were recorded; six of them have not been recorded before. All faces in the [001] zone are striated along crystallographic axis c. All striated forms in the [001] zone exhibit multiple signals. Two of the signals observed on the form {110} are always very clear. There is an exception on one crystal where just one face, (110), exhibits only one clear signal. Five groups of habits were recorded, two of them new to this mineral species. Eleven samples were examined by X-ray diffraction for calculation of the unit cell parameters yielding a=11.201(1)–11.255(2) Å, b=10.1415(5)–10.155(1) Å, c=7.0885(7)–7.119(2) Å and b=97.431(7)–97.34(1) °. All X-ray diffraction patterns show a peculiarity: some diffraction lines are widened or doubled with the appearance of additional diffraction lines systematically on lower °2Q. These diffraction lines have smaller intensities and cannot be indexed in accordance with brazilianite crystal structure.Četrdeset i četiri kristala brazilijanita s nekoliko lokaliteta iz Brazila, Ruande i Kanade je mjereno na dvokružnom refleksnom goniometru u svrhu određivanja morfologije. Zabilježeno je 20 formi, od kojih šest do sada nije opisano. Sve plohe u zoni [001] su prutane paralelno kristalografskoj osi c. Sve prutane forme u [001] zoni daju višestruke signale. Forma {110} daje višestruke signale od kojih su dva uvijek oštra. Postoji iznimka gdje na jednom kristalu samo jedna ploha, (110), daje samo jedan oštar signal. Zabilježeno je pet grupa habitusa od kojih dva nova za ovu mineralnu vrstu. Jedanaest uzoraka je snimljeno rentgenskom difrakcijom da bi se izračunali parametri jedinične ćelije: a=11.201(1)-11.255(2) Å, b=10.1415(5)-10.155(1) Å, c=7.0885(7)-7.119(2) Å i b=97.431(7)-97.34(1)°. Svi rentgenogrami pokazuju zanimljivost: neke difrakcijske linije su proširene ili podvostručene s pojavom dodatnih difrakcijskih linija sustavno na nižim °2Q. Ove difrakcijske linije su manjeg intenziteta te se ne mogu indicirati u skladu s kristalnom strukturom brazilijanita

Mineraloške zbirke u nastavi

Mineraloške zbirke mogu biti različitog tipa, a količina i raznovrsnost uzoraka ovisit će o mogućnostima samog kolekcionara, kao i o dostupnosti uzoraka. Samo prikupljanje uzoraka je trajan proces, za koji je potrebno predznanje o mineralima koji se sakupljaju, ponajprije o njihovim fizičkim svojstvima kao prvim obilježjima koja se opažaju na nekom uzorku. U tekstu je u kratkim crticama izneseno kako formirati reprezentativnu mineralošku zbirku, kako ju obraditi, čuvati te upotrijebiti u nastavi

The hydrothermal recrystallization of metamict allanite-(Ce

ABsTrACT Samples of metamict allanite-(Ce) originating from granite pegmatites were recrystallized by heating in air and under hydrothermal conditions. Recrystallization in air resulted in partial recovery of the crystal structure at 650°C. Heating at higher temperatures resulted in decomposition of the allanite structure to a multiphase assemblage containing hematite, cerianite, feldspar, britholite and thorianite. To our knowledge, this is the first report of thorianite as a breakdown product of allanite in literature. The collapse of the structure is mainly related to the removal of structural H 2 O. Recrystallization under hydrothermal conditions yielded a more rapid and complete recovery of the structure at lower temperatures, without the appearance of additional phases. The stability of the allanite structure during hydrothermal recrystallization is related to the retention of OH -groups, available because of the aqueous environment of recrystallization. Also, H 2 O promotes a more rapid and efficient recrystallization due to the enhanced diffusion of cations. Crystallite size and strain calculation also record evidence of the recovery of the structure of damaged allanite. Keywords: allanite-(Ce), metamictization, hydrothermal recrystallization, X-ray diffraction, granitic pegmatites. sOmmAIre Nous documentons la recristallisation de l'allanite-(Ce) prélevée de pegmatites granitiques par chauffage dans l'air et sous conditions hydrothermales. Dans l'air, la recristallisation permet de récupérer partiellement la structure à 650°C. Un chauffage à températures plus élevées mène à la déstabilisation de la structure pour donner un assemblage multiphasé contenant hématite, cérianite, feldspath, britholite et thorianite. A notre connaissance, ce serait la première fois que la thorianite figure parmi les produits de déstabilisation de l'allanite. La destruction de la structure est surtout liée à l'élimination de H 2 O comme composant structural. Un traitement hydrothermal mène à une recristallisation plus rapide et plus complète de la structure, et à des températures plus faibles, sans formation de phases additionnelles. La stabilité de la structure de l'allanite-(Ce) au cours de la recristallisation hydrothermale est liée à la préservation des groupes OH -dans la structure, résultat du milieu aqueux de la recristallisation. Aussi, la présence de H 2 O favorise une transformation plus rapide et efficace à cause de son rôle à faciliter la difusion des cations. La taille des domaines cristallins et l'importance de déformation démontrent aussi le progrès de la recristallisation structurale de l'allanite endommagée. (Traduit par la Rédaction

Chemistry in Teaching: Mineralogical Collections in Teaching

Mineraloške zbirke mogu biti različitog tipa, a količina i raznovrsnost uzoraka ovisit će o mogućnostima samog kolekcionara, kao i o dostupnosti uzoraka. Samo prikupljanje uzoraka je trajan proces, za koji je potrebno predznanje o mineralima koji se sakupljaju, ponajprije o njihovim fizičkim svojstvima kao prvim obilježjima koja se opažaju na nekom uzorku. U tekstu je u kratkim crticama izneseno kako formirati reprezentativnu mineralošku zbirku, kako ju obraditi, čuvati te upotrijebiti u nastavi. Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna.Mineralogical collections are specialized geological collections consisting of mineral samples. They can be of different type, and the number and diversity of samples depend primarily on the possibilities of the collector, i.e. availability of samples. Collecting of samples is a permanent process, which requires prior knowledge of the minerals to be collected, especially of their physical properties as the first features encountered on a sample. Mineral samples are collected in various ways, i.e. through field investigation, by purchase, exchange, or donations. If mineralogical collections are to be used in elementary or high school teaching, they can be smaller and consist of samples collected only in the schools’ vicinity. Mineralogical collections for college education are usually more complex and are based on the crystal-chemical properties of the minerals. A brief introduction about forming a representative mineralogical collection, processing, maintaining, and utilizing it in teaching is given in this article. This work is licensed under a Creative Commons Attribution 4.0 International License

On the origin of iron-cross twins of pyrite from Mt. Katarina, Slovenia

Iron-cross twins of pyrite are well known among mineralogists, however it is quite surprising that the conditions of their formation remain unexplored. To address this question we studied pyrite twins from the Upper Permian silts of Mt. Katarina near Ljubljana (Slovenia), which represent one of the most typical geological environments for twinned pyrite. Mineralization of pyrite starts with a reduction of the primary red-coloured hematite-rich sediment by sulfide-rich fluids that penetrated the strata. A short period of magnetite crystallization is observed prior to pyrite crystallization, which indicates a gradual reduction process. Sulfur isotope analysis of pyrite shows an enrichment in δ34S, suggesting its origin from the neighbouring red-bed deposit. Other sulfides, such as chalcopyrite and galena, formed at the end of pyrite crystallization. Remnants of mineralizing fluids trapped at the interfaces between the inclusions and host pyrite show trace amounts of Pb and Cu, indicating their presence in the solutions throughout the period of pyrite crystallization. An electron microscopy and spectroscopy study of twin boundaries showed that interpenetration twinning is accomplished through a complex 3D intergrowth of primary {110} Cu-rich twin boundaries, and secondary {100} boundaries that are pure. We show that approximately one monolayer of Cu atoms is necessary to stabilize the {110} twin structure. When the source of Cu is interrupted, the two crystal domains continue to form {100} interfaces, that are more favourable for pure pyrite

Crystal morphology and xrd peculiarities of brazilianite from different localities.

Forty four brazilianite crystals from several localities in Brazil, Rwanda and Canada were measured on a two-circle goniometer to determine brazilianite morphology. Twenty forms were recorded; six of them have not been recorded before. All faces in the [001] zone are striated along crystallographic axis c. All striated forms in the [001] zone exhibit multiple signals. Two of the signals observed on the form {110} are always very clear. There is an exception on one crystal where just one face, (110), exhibits only one clear signal. Five groups of habits were recorded, two of them new to this mineral species. Eleven samples were examined by X-ray diffraction for calculation of the unit cell parameters yielding a=11.201(1)–11.255(2) Å, b=10.1415(5)–10.155(1) Å, c=7.0885(7)–7.119(2) Å and b=97.431(7)–97.34(1) °. All X-ray diffraction patterns show a peculiarity: some diffraction lines are widened or doubled with the appearance of additional diffraction lines systematically on lower °2Q. These diffraction lines have smaller intensities and cannot be indexed in accordance with brazilianite crystal structure

Rare Earth Elements Enrichment in the Upper Eocene Tošići-Dujići Bauxite Deposit, Croatia, and Relation to REE Mineralogy, Parent Material and Weathering Pattern

Tošići-Dujići bauxite deposit, situated in Dalmatian inlands, Croatia, contains minor remaining bauxite reserves. The deposit lies on Lower Eocene foraminiferal limestone and is covered by Upper Eocene Promina sediments. Bauxite samples were analyzed for textural, mineralogical, and geochemical features in order to determine absolute REE abundances and their relation to mineralogy, as well as to devise the origin of REE enrichment and to trace weathering and bauxitization paths of the parent material. The samples show total REE abundances up to 3500 mg/kg with significant HREE enrichment in some cases. All samples are gibbsitic with hematite and anatase as major phases. Kaolinite occurs in most of the samples, and goethite, böhmite, and nordstrandite are minor phases. Monazite-(Ce) and xenotime-(Y) were identified as detrital REE minerals as well as authigenic florencite-(Ce). In the REE most abundant sample, REE are most likely bound to Fe- and Ti-oxide phases as suggested by correlation analysis. Chemical weathering proxies show intensive weathering. Geochemical and textural data imply that the REE enrichment is influenced by intensive weathering (CIA 97.87–99.26) of detrital material, and also by possible deposition/redeposition of residual material potentially derived and mobilized from various sedimentary rocks of the area