Dissolution-Repackaging of Hellandite-(Ce), Mottanaite-(Ce)/Ferri-Mottanaite-(Ce)
Maria Grazia PernaDaria ZaccariaGianluigi RosatelliFrancesco Saverio StoppaniEzio CurtiJohn SprattEmma Humphreys‐WilliamsJens NajorkaWill BrownscombeFabrizio NestolaFrancesco Stoppa
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Abstract:
We investigated hellandite-group mineral phases from the Roman Region, alkali syenite ejecta, by multimethod analyses. They show a complex crystallisation history including co-precipitation of hellandite-(Ce) with brockite, resorption, sub-solidus substitution with mottanaite-(Ce), exsolution of perthite-like ferri-mottanaite-(Ce), overgrowth of an oscillatory-zoned euhedral shell of ferri-mottanaite-(Ce) and late, secondary precipitation of pyrochlore in the cribrose hellandite-(Ce) core. LREE/HREE crossover and a negative Eu anomaly in hellandite-group minerals follows fO2 increase during magma cooling. The distinction among the hellandite-group minerals is based on the element distribution in the M1, M2, M3, M4 and T sites. Additional information on miscibility relationship among the hellandite sensu strictu, tadzhikite, mottanaite, ferri-mottanaite and ciprianiite endmembers derives from molar fraction calculation. We observed that change in composition of hellandite-group minerals mimic the ligands activity in carbothermal-hydrothermal fluids related to carbonatitic magmatism.Keywords:
Analcime
Nepheline
Amphibole
Amphibole
Nepheline
Nepheline syenite
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Sodium analcime (nepheline) phonolites in Mibale area of Tibetan Plateau contain abundant clinopyroxene phenocrysts which show the normal, reverse or oscillatory zoning patterns. The normal zones increase in FeO, Na2O, Al2O3 and TiO2 but decrease in Mg#, MgO, Cr2O3 from core to rim, which indicates the normal magmatic evolution of fractional crystallization. The reverse zone have increasing Mg#, MgO and Cr2O3 but decreasing FeO, Na2O and Al2O3, indicating that the sodium analcime (nepheline) phonolite had been mixed or contaminated by the ultra-potassic or potassic magmas, and that both phonolite and potassic-rich rocks might have different parental magmas. The clinopyroxenes with oscillatory zones were probably the result of multi-stage magmatic mixing since that Na2O, Al2O3, TiO2 and Cr2O3 vary between normal and reverse zone clinopyroxenes as well as Mg# within the range of the phenocryst and the matrix clinopyroxenes. The peralkaline sodium magmas erupted at 13~12Ma in the area, corresponding to a temporary tectonic transformation, which suggests a typical intracontinental extensional setting.
Phenocryst
Nepheline
Analcime
Peralkaline rock
Fractional crystallization (geology)
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Amphibole
Nepheline
Nepheline syenite
Magma chamber
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Various Na-bearing Be silicates occur in late-stage veins and in alkaline rocks metasomatised by late-magmatic fluids of the Ilímaussaq alkaline complex in South Greenland. First, chkalovite crystallised with sodalite around 600°C at 1 kbar. Late-magmatic assemblages formed between 400 and 200°C and replaced chkalovite or grew in later veins from an H2O-rich fluid. This fluid is also recorded in secondary fluid inclusions in most Ilímaussaq nepheline syenites. The late assemblages comprise chkalovite + ussingite, tugtupite + analcime ± albite, epididymite + albite, bertrandite ± beryllite + analcime, and sphaerobertrandite + albite or analcime(?). Quantitative phase diagrams involving minerals of the Na–Al–Si–O–H–Cl system and various Be minerals show that tugtupite co-exists at 400°C only with very Na-rich or very alkalic fluids [log (aNa+/aH+) > 6–8; log (aBe2+/(aH+)2) > –3]. The abundance of Na-rich minerals and of the NaOH-bearing silicate ussingite indicates the importance of both of these parameters. Water activity and silica activity in these fluids were in the range 0.7–1 and 0.05–0.3, and XNaCl in a binary hydrous fluid was below 0.2 at 400°C. As bertrandite is only stable at < 220°C at 1 kbar, the rare formation of epididymite, eudidymite, bertrandite and sphaerobertrandite by chkalovite-consuming reactions occurred at still lower temperatures and possibly involved fluids of higher silica activity.
Analcime
Nepheline
Sodalite
Leucite
Nepheline syenite
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In the present paper the mineralogy and petrological importance of some minerals from the nepheline syenites of South Greenland are discussed. The firstnamed mineral, igalikite, is from the Igaliko batholith, the remainder are from the Ilímaussaq batholith (see Ussing, 33). Igalikite was described by Bøggild from a boulder collected near Igaliko. On re-examination of this mineral it was shown to be a pseudomorph of analcime and "gieseckite" after nepheline. Naujakasite was described by Bøggild from a boulder collected at Naujakasik. The mineral has now been found in lujavrite at Tuperssuatsiaq and in the northern part of the Ilimaussaq batholith. Monazite in small clusters of angular grains are quite common in the lujavrites. The erikite described by Bøggild is shown to be a mixture of monazite and analcime and/or natrolite. Britholite has been found as small crystals in a number of altered lujavrites. Monazite and britholite are both considered to be formed at the expense of the material set free during the alteration of the eudialyte of the nepheline syenites. Neptunite in macroscopic grains is rare, but the mineral is commonly seen in thin sections, especially in rocks with altered eudialyte. The neptunite was probably formed during hydrothermal alteration of the eudialyte. A white mineral has been found at Igdlunguaq associated with neptunite, epistolite and analcime. The mineral has a primitive cubic unit cell and is probably a Na- and Nb-rich perovskite mineral. A more detailed description of this possibly new mineral will be undertaken when a chemical analysis has been carried out. Ussingite was described by Bøggild from boulders. It has now been found in place at the head of Kangerdluarssuk where it occurs in a recrystallized zone of deformation in naujaite. It is associated with steenstrupine, lovozerite (?), and ægirine and is secondary after microcline and sodalite. Lovozerite(?) a mineral resembling the lovozerite of the Kola peninsula has been found associated with the ussingite of Kangerdluarssuk and also with eudialyte in lujavrite. It is interpreted as a secondary mineral after eudialyte. Epistolite is according to a preliminary examination a member of an isomorphous series of which the murmanite of the Kola peninsula is another member.
Nepheline
Batholith
Analcime
Nepheline syenite
Leucite
Titanite
Pseudomorph
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Abstract Hydrothermal analcime synthesis at 10 MPa isobar and 100, 200, and 300 °C isotherms was performed. As synthesis initial components the minerals nepheline, albite, natrolite, jadeite, wairakite and the mixtures nepheline + albite and nepheline + natrolite were used. 1 M Na 2 SiO 3 , 1 M NaCl and 0.1 M NaOH ( p H = 14, 7, 13) solutions were applied as the hydrothermal medium. On evaluating the synthesis products by means of X‐ray diffraction analysis and X‐ray microanalysis (EDAX) it was estimated that different analcime structural modifications originate especially at temperatures above 200 °C in neutral and alkaline medium from all the mentioned minerals. Analcime with a higher symmetry of the unit cell of crystals form at temperatures above 250 °C particularly.
Nepheline
Analcime
Nepheline syenite
Andradite
Grossular
Hydrothermal Synthesis
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Jadeitite from the Itoigawa–Omi area in the Hida–Gaien belt is hydrothermal in origin, occurring as tectonic blocks in a serpentinite mélange. Most jadeitite shows bimineralic mineralogy essentially composed of jadeite and albite without quartz. It sometimes has veins and cavities filled with zeolite–bearing assemblages of natrolite–jadeite and analcime–jadeite. In veins and cavities, jadeite often shows euhedral shapes in natrolite and analcime matrices and accompanies Sr–Ti–Zr–bearing new minerals such as itoigawaite, rengeite, and matsubaraite. Phase relation in the NaAlSiO4–SiO2–H2O system has been analyzed based on the Schreinemakers’ rule to explain the hydrothermal origin of these jadeitites and the euhedral form of jadeite. The albite– and natrolite–jadeitites were precipitated from a hydrothermal fluid in the pressure–temperature field surrounded by the following four reactions: 1) albite = jadeite + quartz, 2) natrolite = nepheline + jadeite + 2 water, 3) natrolite + albite = 3 jadeite + 2 water, and 4) analcime = jadeite + water. Jadeite and analcite seem to be in equilibrium because of their euhedral shapes, but never crystallize from a fluid phase in the NaAlSiO4–SiO2–H2O system. To explain the presence of euhedral jadeite in an analcime matrix, we propose two possible interpretations: 1) that the introduction of evolved, multicomponent, hydrothermal fluid becomes the fluid–analcime–jadeite triangle and appears in a pseudo–ternary system and 2) that hydrothermal fluid was present in an amount insufficient to form a water–saturated, analcime–bearing assemblage.
Analcime
Nepheline
Leucite
Paragenesis
Chalcedony
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Mixtures of nepheline, quartz, and halite react in the presence of water at 1 kbar total pressure. Depending on bulk composition, subsolidus assemblages-all coexisting with vapor and/or aqueous liquid-are: quartz-albite-halite, albite-sodalite-halite, nepheline-albite-sodalite, nepheline-sodalite. Below 550°C, analcime appears, permitting the assemblages albite-analcime-sodalite, analcime-sodalite, and nepheline-analcime-sodalite. Below 625°C, a supercritical saline fluid coexists with solid phases; when the mole fraction of NaCl in this fluid is high, analcime cannot form. Above 625°C, an aqueous vapor coexists with a dense $$NaCl-H_{2}O$$ liquid; the vapor contains little NaCl and $$P_{H2O}$$ approximates $$P_{total}$$. Natrolite and the NaCl end-member of the scapolite series were not encountered. Eutectic melting between quartz and albite occurs at $$Ab_{63}Qz_{37}$$ at $$765^{\circ} \pm 10^{\circ}C$$, and appears to be independent of the presence or absence of NaCl. Above 700°C in the silica-oversaturated portion of the system, sodium chloride reacts with quartz and water to produce HCl and presumably a sodium silicate, although the latter was not found. The presence of NaCl in the nepheline-normative part of the system stabilizes sodalite; in the quartz-normative part, it has no perceptible effect upon silicate phase relations above the solidus, because NaCl-rich liquid is immiscible with silicate melt. The experimental results do not support speculations that alkalic rocks can form by anatexis or assimilation of sedimentary sequences containing halite.
Nepheline
Analcime
Sodalite
Halite
Grossular
Sanidine
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