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

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

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

Yugoslavia energy and protein feeding standards for growing and fattening cattle

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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