Aluminous Diopside Research Articles

Petrogenesis of Cenozoic high-Mg (picritic) volcanic rocks in the České středohoří Mts. (Bohemian Massif, Czech Republic)

Representative samples of high-Mg (picritic) rocks of Eocene to Oligocene age (38 to 21 Ma) from the Ceske středohoři Mts. (CSM) in the Ohře/Eger Rift were studied and compared with Cenozoic high-Mg rocks from the Bohemian Massif. The picritic rocks of the CSM correspond to picrite, meimechite and basanite to tephrite. Individual petrographic types are characterised by the association of mafic minerals: magnesian olivine (Fo86–80) + clinopyroxene (aluminian diopside) ± amphibole (pargasite/kaersutite) ± dark mica (ferroan phlogopite). The contents of incompatible elements, such as Nb, Ta, U, Th, the LaN/YbN ratios, and the overall Sr–Nd–Pb isotope signatures of the high-Mg rocks partly overlap the basanites of the Usti Formation, also showing a similar age (44–21 Ma). The Pb isotope signature for all recognised high-Mg rock types is compatible with a variable contribution from an inherited (Variscan) orogenic Pb component preserved in their lithospheric mantle source. Both the high-Mg volcanic rocks from the CSM and from other areas of the Bohemian Massif require the involvement of a heterogenous lithospheric source. Their parental melts were generated by variable degree of melting of an olivine-rich peridotitic mantle, containing clinopyroxene–amphibole (± phlogopite) vein assemblages with highly radiogenic Sr and Pb signatures.

Refractory inclusions in the pristine carbonaceous chondrites DOM 08004 and DOM 08006

AbstractThe Antarctic carbonaceous chondrites DOM 08004 and DOM 08006 have been paired and classified as CO3.0s. There is some uncertainty as to whether they should be paired and whether they are best classified as CO chondrites, but they provide an opportunity for the study of refractory inclusions that have not been modified by parent body processes. In this work, refractory inclusions in thin sections of DOM 08004 and 08006 are studied and compared with inclusions in ALHA77307 (CO3.0) and Acfer 094 (C3.0, ungrouped). Results show that the DOM samples have refractory inclusion populations that are similar to each other but not typical of CO3 chondrites; main differences are that the DOM samples are slightly richer in inclusions in general and, more specifically, in the proportions of grossite‐bearing inclusions. In DOM 08004 and DOM 08006, 12.4% and 6.6%, respectively, of the inclusions are grossite‐bearing. This is higher than the proportion found in Acfer 094 (5.2%), whereas none were found in ALHA77307. Like those in Acfer 094, DOM inclusions are small (mostly <100 μm across) and fine‐grained, and thin rims of aluminous diopside±melilite are very common. Also like Acfer 094, most phases in the DOM inclusions have FeO contents higher than expected for primary refractory phases. In addition to typical inclusions, some unusual ones were found in DOM 08004, including a perovskite‐rich one with a rare, recently reported Sc‐, Al‐oxide and davisite; a very grossite‐rich inclusion with a small, hibonite‐rich core enclosed in a grossite mantle; and a relict, grossite‐rich inclusion enclosed in an Al‐rich chondrule. The CAI populations in the DOM samples are similar to each other and, based on grossite abundances, FeO enrichments and occurrences of rims are more Acfer 094‐like than CO3‐like. An earlier history on an FeO‐rich parent was previously favored over nebular equilibria or in situ reactions to account for FeO enrichments in CAIs in the otherwise pristine chondrite Acfer 094, and a similar history is indicated for the DOM CAIs. Acfer 094, DOM 08004 and 08006 might best be classified as a new subgroup of CO3 chondrites.

SERENDIBITE, A COMPLEX BOROSILICATE MINERAL FROM PONTIAC, QUEBEC: DESCRIPTION, CHEMICAL COMPOSITION, AND CRYSTALLOGRAPHIC DATA

Serendibite has been recently discovered in the Portage-du-Fort area, Pontiac Regional County Municipality, Quebec. Dark blue, often polysynthetic twinned on {011} and with no cleavage, serendibite crystals occur exclusively in a calc-silicate rock. Fine-grained anhedral serendibite, sometimes poikiloblastic, occurs with aluminous diopside. Less commonly, serendibite may form decussate masses in the same rock type. Serendibite is biaxial negative, with indices of refraction α 1.685(2), β 1.700(2), and γ 1.712(2); 2 V meas. = 93.6(4)°, 2 V calc. = 91°. Orientation matrix is X ^ c = +20.5°, Y ^ b = −42.6°, and Z ^ a = −24.6°. Dispersion is strong, r with cell parameters refined from an X-ray powder-diffraction pattern: a 10.035(2), b 10.423(3), c 8.648 (2) A, α 106.47(3)°, β 95.91(2)°, γ 124.46(2)°, V 674.3(2) A3. The seven strongest lines of the X-ray powder diffraction pattern [ d in A( I )( hkl )] are: 3.328(45)( ![Formula][2] 230), 3.029 (96)(012, 021, ![Formula][3] ![Formula][4] 2), 2.854(96)(0 ![Formula][5] 3, 0 ![Formula][6] 1, 120), 2.689(29)(3 ![Formula][7] 1), 2.604(95)(030), 2.469(100)( ![Formula][8] ![Formula][9] 3, 0 ![Formula][10] 3), and 2.357(28)(2 ![Formula][11] 3, 23 ![Formula][12] ). The crystal structure determination refined to R = 2.1% for 3877 unique reflections. The borosilicate structure, a member of the aenigmatite-rhonite group, is composed of layers parallel to (011). Layers of tetrahedral chains cross-linked by octahedral polyhedra alternate with layers of octahedral chains cross-linked by square antiprism polyhedral sheets. Tetrahedral and octahedral polyhedra are partially ordered and site assignments were determined. All cation sites are disordered to some degree. [1]: /embed/mml-math-1.gif [2]: /embed/mml-math-2.gif [3]: /embed/mml-math-3.gif [4]: /embed/mml-math-4.gif [5]: /embed/mml-math-5.gif [6]: /embed/mml-math-6.gif [7]: /embed/mml-math-7.gif [8]: /embed/mml-math-8.gif [9]: /embed/mml-math-9.gif [10]: /embed/mml-math-10.gif [11]: /embed/mml-math-11.gif [12]: /embed/mml-math-12.gif

Mineralogy and environmental geochemistry of historical iron slag, Hopewell Furnace National Historic Site, Pennsylvania, USA

The Hopewell Furnace National Historic Site in southeastern Pennsylvania, which features an Fe smelter that was operational in the 18th and 19th centuries, is dominated by three slag piles. Pile 1 slag, from the Hopewell Furnace, and pile 2 slag, likely from the nearby Cornwall Furnace, were both produced in cold-blast charcoal-fired smelters. In contrast, pile 3 slag was produced in an anthracite furnace. Ore samples from the nearby Jones and Hopewell mines that fed the smelter are mainly magnetite-rich with some sulfides (pyrite, chalcopyrite, sphalerite) and accessory silicates (quartz, garnet, feldspar, and clay minerals). Slag piles 1 and 2 are similar mineralogically containing predominantly skeletal and dendritic aluminian diopside and augite, skeletal forsteritic olivine, glass, rounded blebs of metallic Fe, and exotic quartz. Olivine is a major phase in all samples from pile 2, whereas it occurs in only a few samples from pile 1. Samples of the <2 mm-size fraction of surface composite slag material or crushed slag from at depth in piles 1 and 2 are mineralogically similar to the large surface slag fragments from those piles with the addition of phases such as feldspars, Fe oxides, and clay minerals that are either secondary weathering products or entrained from the underlying bedrock. Pile 3 slag contains mostly skeletal forsteritic olivine and Ti-bearing aluminian diopside, dendritic or fine-grained subhedral melilite, glass, euhedral spinel, metallic Fe, alabandite–oldhamite solid solution, as well as a sparse Ti carbonitride phase. The bulk chemistry of the slag is dominated by Al2O3 (8.5–16.2 wt.%), CaO (8.2–26.2 wt.%), MgO (4.2–24.7 wt.%), and SiO2 (36.4–59.8 wt.%), constituting between 81% and 97% of the mass of the samples. Piles 1 and 2 are chemically similar; pile 1 slag overall contains the highest Fe2O3, K2O and MnO, and the lowest MgO concentrations. Pile 3 slag is high in Al2O3, CaO and S, and low in Fe2O3, K2O and SiO2 compared to the other piles. In general, piles 1 and 2 are chemically similar to each other, whereas pile 3 is distinct – a conclusion that reflects their mineralogy. The similarities and differences among piles in terms of mineralogy and major element chemistry result from the different smelting conditions under which the slag formed and include the fuel source, the composition of the ore and flux, the type of blast (cold versus hot), which affects the furnace temperature, and other beneficiation methods. The three distinct slag piles at Hopewell are enriched in numerous trace elements, such as As (up to 12 mg/kg), Cd (up to 0.4 mg/kg), Co (up to 31.8 mg/kg), Cu (up to 647 mg/kg), Mn (up to 0.69 wt.%), Pb (up to 172 mg/kg) and Zn (up to 393 mg/kg), together with Fe (13.9 wt.%), when compared to the average for the continental crust, with the <2 mm-size fraction commonly containing the highest concentrations. Enrichments in various elements (e.g., Cd, Co, Cu, Pb, Zn) were also found in the ore samples. Despite these enrichments, comparison of bulk chemistry trace-element concentrations to the environmental guidelines suggests most elements are likely not problematic with the exception of As, Co, Fe and Mn. Leachate tests that simulate weathering indicate Fe (up to 973 μg/L) and Mn (up to 133 μg/L) are readily released in potentially harmful concentrations compared to secondary drinking water and some aquatic ecosystem toxicity criteria. Aluminum and Cu, although not high in the solid compared to environmental guidelines, also exceed relevant criteria in leachate extracts with maximum concentrations of 2700 μg/L and 17.7 μg/L, respectively. In contrast, As and Co, which are significant in the solids, are not leached in concentrations that exceed guidelines (i.e., 3 μg/L or less for both elements). The weathering rates of the Fe metal and Fe oxides, which host Cu and some Fe, are likely higher than the silicate glass, which hosts the majority of Al, Mn and some Fe, and the crystalline silicates and spinels affecting which elements and how much are released into the environment and surrounding aquatic ecosystem. The mineral assemblages and their chemical composition, the bulk sample chemistry, and leachability of trace elements are all important components in understanding the potential environmental impacts of the slag piles.

AKERMANITE BREAKDOWN TO A CUSPIDINE-BEARING SYMPLECTITE IN A CALC-SILICATE XENOLITH, KIGLAPAIT INTRUSION, LABRADOR, CANADA

We report here an occurrence of cuspidine as part of a complex symplectitic intergrowth formed from the breakdown of akermanite ( X Mg = 0.97, Na-mel 12 Gh 3 ) in a calc-silicate xenolith in the Kiglapait Intrusion, Labrador, Canada. The symplectite is dominated by aluminian diopside, cuspidine, and monticellite, but also contains a calcic garnet (Grs 70 ) and serpentine. Cuspidine approaches closely the ideal F-bearing composition. Average proportions of phases in the intergrowth are 33% clinopyroxene, 27% cuspidine, 21% monticellite, 9% garnet, and 9% serpentine. A reconstructed bulk-composition of the intergrowth approximately matches the composition of the adjacent akermanite, with the exception of Na and Fe, which were probably mobile (or retained in residual akermanite in the case of Na). The dominant phases in the intergrowth probably resulted from progress of the reaction: akermanite + F = diopside + cuspidine + monticellite, with additional grossular forming from the gehlenite component of melilite. Serpentine formed in a later stage of retrogression, once sufficient H 2 O was available. The peak T experienced by the xenolith is well constrained at ≥875°C, but the retrograde, symplectite-forming reaction is less certain (probably ≤700°C), with serpentine forming at an even lower T. Fluorine-rich cuspidine requires interaction with a F-bearing fluid, probably derived from the surrounding magma. This interpretation is consistent with the known volatile content of the Kiglapait Intrusion, which contained F far in excess of H 2 O and Cl.

Thermal behaviour of ‘metamorphic vermiculite’ in Ca-rich ancient ceramic sherds and experimental ceramics

AbstractA ‘metamorphic vermiculite’-like phase was identified in Ca-rich ancient ceramic sherds from excavations in NW Peloponnese, Greece. Archaeometric investigations have shown that the raw materials used in the production of ancient ceramics were derived from local Plio-Pleistocene sediments. Analysis by X-ray diffraction and scanning electron microscopy-energy dispersive spectroscopy showed that ‘metamorphic vermiculite’ is a common constituent phase of these sediments occurring in three texturally different types: as interstratified white mica-chlorite and chlorite-vermiculite, and white mica-(white mica-chlorite) stacks. In an attempt to elucidate the thermal transformation of ‘metamorphic vermiculite’ present in the calcareous raw materials, we produced experimental ceramics made from these local raw materials and fired them at 700, 750, 850, 950 and 1050°C in a static air furnace. The mixed-layered chlorite-vermiculite was transformed completely at ∼800°C contributing to the formation of new high-T minerals. The two other types of ‘metamorphic vermiculite’ retain their original lath-like shape up to 1050°C and only a few crystals show that they have undergone complete transformation at this temperature. In the latter crystals, numerous nanocrystals were formed sub-parallel to the former cleavages of ‘metamorphic vermiculite’ pseudomorphs, suggesting their contribution to the nucleation of high-T minerals (i.e. ferrian aluminian diopside, spinel, Fe oxides) by reactions with the available CaO. It is suggested that the firing conditions (i.e. maximum reaction temperature of 1050°C, reaction time of 1 h, oxygen atmosphere) which promote disequilibrium reactions, and the greater contribution of the white mica constituent against chlorite in some of the initial structures of ‘metamorphic vermiculite’ may be responsible for the delay of its thermal decomposition at 1050°C.

Crystal Nucleation and Growth Rates, Time-Temperature Transformation Diagram, and Mechanical Properties of a SiO2-Al2O3-CaO-MgO-(R2O) Glass in the Presence of Cr2O3, Fe2O3, and TiO2 Nucleants

The crystallization of a SiO2–Al2O3–CaO–MgO–(R2O) glass in the presence of Cr2O3, Fe2O3, and TiO2 nucleants was investigated utilizing differential thermal analyses, X-ray diffraction, and scanning electron microscope. The optimum nucleation and growth rates of aluminian diopside crystals was determined for the most promising glass specimen containing all three nucleants as 1018 m3/s and 6.17 ± 0.55 × 10−9 m/s, respectively. A time–temperature transformation (TTT) diagram was also constructed for 82 wt% crystallization for the above glass sample and a nose time of ≈55 min was obtained. The bending strength of some heat-treated specimens were also determined and were related to crystallization behavior and microstructures. The highest strength value obtained was 166 ± 6 MPa.

The formation of boundary clinopyroxenes and associated glass veins in type B1 CAIs

Abstract— We used focused ion beam thin section preparation and scanning transmission electron microscopy (FIB/STEM) to examine the interfacial region between spinel and host melilite for spinel grains in type B1 inclusions from the Allende and Leoville carbonaceous chondrites. Boundary clinopyroxenes decorating spinel surfaces have compositions similar to those of coarser clinopyroxenes from the same region of the inclusion, suggesting little movement after formation. Host melilite displays no anomalous compositions near the interface and late‐stage minerals are not observed, suggesting that boundary pyroxenes did not form by crystallization of residual liquid. Allende spinels display either direct spinel‐melilite contact or an intervening boundary clinopyroxene between the two phases. Spinel‐melilite interfacial regions in a Leoville B1 are more complex, with boundary clinopyroxene, as observed in Allende, but also variable amounts of glass, secondary calcite, perovskite, and an Mg‐, Al‐, OH‐rich and Ca‐, Si‐poor crystalline phase that may be a layered double hydrate. One possible scenario of formation for the glass veins is that open system alteration of melilite produced a porous, hydrated aggregate of Mg‐carpholite or sudoite + aluminous diopside that was shock melted and quenched to a glass. The hydrated crystalline phase we observed may have been a shocked remnant of the precursor phase assemblage, but is more likely to have formed later by alteration of the glass.In the mantle, boundary clinopyroxenes may have been crystallized from Ti‐rich liquids formed by the direct dissolution of perovskite and an associated Sc‐Zr‐rich phase or as a reaction product between dissolving perovskite and liquid. In the core, any perovskite and associated Ti‐enriched liquids that may have originally been present disappeared before the growth of boundary clinopyroxene, and the observed boundary clinopyroxene may have nucleated and grown from the liquid, along with the larger core clinopyroxene.

Radiation damage in diopside and calcite crystals from uranothorianite inclusions

Combining observation and simulation, radiohalos formed around uranothorianite (UTh) from the Tranomaro granulitic skarns (SE-Madagascar) were studied. These structures consist of UTh grains surrounded by both aluminous diopside (Cpx) and calcite (Cc 1) crystals. Optical microscope and Scanning Electron Microscope (SEM) images revealed (1) the presence of radiating cracks around the UTh probably due to swelling of the metamict UTh, (2) a diffuse optical halo at the Cc 1/UTh interface, and (3) a wide “reaction zone” at the Cpx/UTh interface, composed of “secondary calcite” (Cc 2) with low temperature sheet silicate from the smectite (φ) group. Samples prepared across various interfaces using Focused Ion Beam (FIB) were investigated by Transmission Electron Microscope (TEM). In contrast to SEM observations, there is no direct contact between Cc 1 and UTh. From Cc 1 to UTh, we found: (1) a large (~ 200–300 nm) amorphous zone (A), enriched in U, Th and Ca, but without Si; (2) a chain (B) of very small (~ 20 nm) ThO 2 crystals; (3) another amorphous zone (C), which, in contrast to zone A is enriched in Si; and (4) another zone (D) made of small amorphous Si-rich “bubbles”. The organization is similar for the UTh–Cc 2 interface. The presence of hydrous minerals (smectite) and carbonate (calcite) in reaction zone and in cracks, the presence of Pb-rich inclusions in secondary calcite, the abundance of fluid inclusions in the porous layer in calcite, the dissociation of U and Th in the calcite–uranothorianite layer, and the ThO 2 chains along interfaces, are strong indications that low-temperature crystallization was promoted by a fluid phase. SRIM simulation was used to calculate the effect of α and recoil particles of the three decay chains, in Cpx, Cc and UTh. The thickness of the damaged area calculated for α in Cpx and Cc are similar to the widths of the recrystallized areas observed in thin section (~ 30 μm). Corrected with the “wandering recoil effect”, the size of the damaged area calculated for recoil nuclei in Cc (~ 50–60 nm) is ~ multiplied by 3 and is in rather good agreement with the thickness of the totally amorphous layer at the Cc–UTh interface (~ 200 nm). Finally, it is emphasized that radiohalos are a point of chemical and physical weakness in a rock and probably a starting point for alteration.

The Lages diatremes: mineral composition and petrological implications

Chemical data of heavy minerals from Lages diatremes in southern Brazil have been studied with the aim of characterizing the sample source(s). Three groups of minerals are recognized: I) aluminian-chromian pyroxene, pyrope garnet and chromian spinel, which represent disaggregated fragments of spinel, spinel+garnet and garnet facies peridotite; II) low-Cr aluminian pyroxene that occurs as megacrysts are high pressure phases (7-12 kb) being crystallized from an alkaline-like evolving magma; III) low-Cr aluminian diopside of crustal origin. Evidence of carbonatitic cryptic metasomatic enrichment is shown by clinopyroxenes of Groups I and II. The data do not support a kimberlitic affinity as it has been suggested for the diatremes. Rather, they are interpreted as vents related to the alkaline magmatism affecting the area in Late Cretaceous. The alkaline parental magma of the pyroxene megacrysts was generated from a metasomatized mantle at garnet facies that incorporated fragments of the surrounding still fertile mantle. Presumably at spinel-facies level the magma began to fractionate the megacrysts, whose crystallization proceeded over a large range of falling pressure and temperature. The chemical similarities between Group III clinopyroxenes and those from the differentiated lithotypes indicate that the magma carried this mineral phase on its evolution, at crustal conditions, towards a more evolved alkaline composition. Still, a non-cognate origin for the Group III clinopyroxenes cannot be discarded.

Structural characterization of basalt-based glass–ceramic coatings

There are a lot of technologically interesting characteristics of glass–ceramics, which are hard, wear resistant, oxidation and corrosion resistant ceramic materials. In the present study, the production of the basalt-based glass–ceramic coating by atmospheric plasma spray technique and their structural characterization were reported. Basalt-based glass coating was performed on AISI 1040 steel substrate which was pre-coated with Ni–5 wt% Al by using plasma spray gun. Basalt coatings of the glass form were crystallized at 800, 900 and 1000 °C for 1–4 h in orders to transform to the glass–ceramic structure. The presence of augite [(CaFeMg)SiO 3], diopside [Ca(Mg 0.15Fe 0.85)(SiO 3) 2] and aluminian diopside [Ca(Mg,Al)(Si,Al) 2O 6] crystalline phases formed in the basalt-based glass–ceramic coating layer was detected by X-ray diffraction analysis. Optical microscopy with micrometer was used for metallographic examinations. Differential scanning calorimeter was used for determining the crystallization temperature of glass form basalt-based coatings. Microhardness measurements were carried out on the basalt-based glass–ceramic coating layer with Vickers indenter. The hardness of coating layers is changing between 1009 and 1295 HV 0.05 depending on crystallization temperature and process times. It was found that, the higher the crystallization temperature, the more the crystalline phases were resulted. In addition, the lower the crystallization temperature and the longer the treatment time, the harder the coating layer became.

Crystal Structure of the SFCAM Phase Ca2(Ca,Fe,Mg,Al)6(Fe,Al,Si)6O20

The crystal structures of Mg-rich SFCA (SFCAM); Ca2(Ca0.10Mg1.20Fe5.55Si1.50Al3.65)O20 (triclinic P1, a=8.848(1) A, b=9.812(1) A, c=10.403(1) A, α=64.35(1)°, β=84.19(1)°, γ=66.27(1)°, V=742.4(1) A3, Z=2) and Ca2(Mg2.00Fe4.45Si2.15Al3.40)O20 (triclinic P1, a=8.928(2) A, b=9.823(2) A, c=10.389(1) A, α=64.41(1)°, β=83.90(1)°, γ=65.69(1)°, V=746.0(2) A3, Z=2) were determined by the single crystal X-ray diffraction. The structure of SFCAM is iso-structural with aenigmatite and well demonstrated by an alternating stacking of the tetrahedral and octahedral layers. The tetrahedral sites of oxygen are occupied either by Fe, Al and Si. The octahedral sites of oxygen are occupied either by Fe, Mg and Al and this feature contrasts with that of the Mg-free SFCA phase where Al prefers tetrahedral sites, only. In particular, Si4+ and Mg2+ prefer the tetrahedral T1, T2 and T4 sites and octahedral M5 and M6 sites, respectively, by producing a structural slab similar to that of aluminous diopside. Such local concentration of divalent Mg2+ and tetravalent Si4+ in the structure of SFCAM is strongly favored in order to compensate the local charge valance. The SFCAM phase indicates the superior structural flexibility for a variety of cations and this feature is promising for the chemical design of the bonding phase in the sinter ore.

The oscillatory intergrowth of feldspars in titanian andradite, Little Dromedary, NSW, Australia

Veins bearing titanian andradite were found in a metasomatically altered clinopyroxenite cumulate of an alkali magmatic suite (Little Dromedary, NSW, Australia). The titanian andradite is up to 2.5 cm in size, mainly subhedral and displays a large concentric, oscillatory intergrowth with layers consisting of plagioclase and alkali feldspar. Detailed field work and petrography showed that there is a gradual change in paragenesis from the cumulitic clinopyroxenite with interstitial plagioclase to an apatite- and scapolite-bearing plagioclase-titanian andradite-pyroxene rock, which hosts the titanian andradite veins. Clinopyroxene composition changes from a magmatic Ti-bearing subsilicic ferrian aluminian diopside to a metamorphic Ti-free, Al-poor diopside. Plagioclase changes composition from oligoclase (Ab 81 An 14 Or 5 ) in the pyroxenite to bytownite (Ab 14 An 86 ) in the garnet-pyroxene rock and to oligoclase (Ab 76 An 21 Or 3 ) in the vein. Orthoclase occurs exclusively in the vein and contains 12% albite component. The titanian andradite-bearing veins and the change in paragenesis, bulk rock and mineral composition provide evidence for the reaction of a late magmatic, oxidizing hydrothermal fluid with the magmatic pyroxenite. The temperature of alteration is constrained by the composition of the coexisting plagioclase and alkali feldspar in titanian andradites to ∼ 420 °C. Crystallization of the titanian andradite indicates that Ti was transported on a metre scale from the magmatic clinopyroxene to the vein by a fluid. Ti solubility may have been enhanced by ligands such as F - , Cl - , PO 4 3- , SO 4 2- and CO 3 2- , which are all present in the fluid as documented by their incorporation in metamorphic apatite, scapolite, and carbonate coexisting with titanian andradite. KCl and NaCl salt inclusions in feldspar within the titanian andradite were found with transmission electron microscopy (TEM) and indicate that the fluid was partly supersaturated in these components. The alternating intergrowth of titanian andradite and feldspars mirrors an oscillating evolution of the fluid. TEM images of the garnet-feldspar interface suggest that garnet has been partly dissolved prior to or during feldspar precipitation, supporting the hypothesis of significantly changing fluid composition during vein formation. The concentric intergrowth is interpreted as the result of both the changing chemistry of the fluid and the different growth behaviour of garnet and feldspar.

Mineralogical and Mössbauer spectroscopic study of a diopside occurring in the marbles of Andranondambo, southern Madagascar

Dark pyroxene crystals found in a calcite vein cutting across marbles and skarns at Andranondambo, southern Madagascar, were investigated with various techniques in order to characterize and identify the mineral phase. Methods applied include powder X-ray diffraction, thin-section microscopy, electron-microprobe analysis, densimetry, and thermogravimetry coupled to mass spectrometry (TGA-MS), FTIR, and Mossbauer spectroscopy. The chemical composition of the mineral phase was determined as {Ca 0 . 9 8 ,Na 0 . 0 3 }[Mg 0 . 6 8 ,Fe 2 + 0 . 0 7 Fe 3 + 0 . 0 3 ,Al 0 . 1 6 ,Ti 0 . 0 4 ](Si 1 . 7 7 ,Al 0 . 2 3 )O 6 . The refined unit-cell parameters are: a = 9.719(2) A, b = 8.838(2) A, c = 5.287(1) A, p = 106.05(2)°. and V = 436.33(6) A 3 . The refractive indices are: α = 1.690 ′ 0.002, β = 1.700 ′ 0.002, and γ = 1.712 ′ 0.002. The density is 3.370 (55) g/cm 3 . The mean refractive index calculated from the chemical composition yields a Mandarino compatibility index of K = -0.0167. From the various analytical data, we were able to conclude that the mineral corresponds to Fe- and Ti-bearing aluminian diopside. TGA-MS data suggest the presence of calcite solid inclusions and minor H 2 O and CO 2 fluid inclusions. Chemical analyses of the calcite host matrix revealed clear rare earth element enrichment. Mossbauer spectra obtained at varying temperatures show the presence of Fe 2 + and Fe 3 + . Both exhibit broad quadrupole-splitting distributions, indicating widely fluctuating chemical and structural environments for the probe Fe nuclei. The broad temperature range (80-470 K) over which the spectra were collected resulted in a precise determination of the Fe 2 + /Fe t o t ratio as 0.68, which is consistent with the chemical composition as determined from the microprobe analyses. For comparison, the Mossbauer spectra of two specimens of the type locality of aluminian diopside (the mineral formerly named fassaite) were analyzed as well and found to be consistent with those obtained for the Madagascar crystals. The relation between mineral paragenesis and local geological features is briefly discussed.

THE MELILITE-BEARING HIGH-TEMPERATURE SKARNS OF THE APUSENI MOUNTAINS, CARPATHIANS, ROMANIA

The melilite-bearing skarns of Cornet Hill (CH) and Upper Cerboaia Valley (UCV), in the Apuseni Mountains of Romania, occur at the contact between monzodiorite bodies of Ypresian age (Paleocene) and Neojurassic calcitic marbles. Typical wollastonite - grossular - diopside endoskarns are separated from exoskarns (tilleyite and spurrite or wollastonite at CH. wollastonite only at UCV), at most places, by a melilite-rich rock, in which veins and vein-like zones of recrystallization are composed only of idiomorphic melilite crystals reaching 15 cm across. Titanian garnet and wollastonite are the principal minerals associated with melilite (and also monticellite, perovskite, vesuvianite, cuspidine. spurrite, tilleyite, calcite, hydroxylellestadite, hydrogrossular and other minor alteration-induced minerals). A different association that includes aluminian diopside and grossular occurs (1) as veinlets in the marble close to the skarns and (2) as relict inclusions in endoskarns. From the geometrical relationships of the zone sequences and the veins, the textural features of the mineral associations and the inferred conditions of fluid-mineral equilibrium, these mineralogical peculiarities are interpreted as resulting from the superposition of two main stages. Firstly, there was circulation of a comparatively CO2-rich fluid formed the early aluminian diopside - grossular endoskarns, with depletion in Si (and Fe, Na, K) and inert behavior of Mg, Al, Ti. Then. a high-temperature (750 degreesC) fluid circulated on both sides of the contact between marble and endoskarns, and developed the melilite-rich, titanian-garnet-bearing rocks partly at the expense of previously formed endoskarns, and spurrite or wollastonite (CH) or wollastonite (UCV) exoskarns at the expense of marble. The pressure of CO2 was very low, less than 26 bars at UCV and 16 bars at CH, with a H2O pressure less than 750 bars. Not only Si and Ca were mobilized, but also Mg, Al and Ti, leached from the endoskarns and deposited in the veins and the nearby part of exoskarns. This stage, which occurred in the temperature range corresponding to the end of the crystallization of plagioclase in the monzodiorite, has pegmatitic chemical and textural features. The main flow of fluid ended with the development of tilleyite partly at the expense of spurrite and wollastonite at CH, and local high-temperature (about 710 degreesC) recrystallization of the zonation, mostly in veins, especially in the endoskarn-exoskarn boundary, but also within the endoskarns. A monticellite - gehlenite association appeared in the melilite-rich rocks, later followed by vesuvianite, whereas in the endoskarn, vesuvianite developed together with coarse-grained wollastonite and grossular.

Refractory inclusions from the ungrouped carbonaceous chondrites MacAlpine Hills 87300 and 88107

Abstract— MacAlpine Hills (MAC) 87300 and 88107 are two unusual carbonaceous chondrites that are intermediate in chemical composition between the CO3 and CM2 meteorite groups. Calcium‐aluminum‐rich inclusions (CAIs) from these two meteorites are mostly spinel‐pyroxene and melilite‐rich (Type A) varieties. Spinel‐pyroxene inclusions have either a banded or nodular texture, with aluminous diopside rimming Fe‐poor spinel. Melilite‐rich inclusions (Åk4–42) are irregular in shape and contain minor spinel (FeO &lt;1 wt%), perovskite and, more rarely, hibonite. The CAIs in MAC 88107 and 87300 are similar in primary mineralogy to CAIs from low petrologic grade CO3 meteorites but differ in that they commonly contain phyllosilicates. The two meteorites also differ somewhat from each other: melilite is more abundant and slightly more Al‐rich in inclusions from MAC 88107 than in those from MAC 87300, and phyllosilicate is more abundant and Mg‐poor in MAC 87300 CAIs relative to that in MAC 88107. These differences suggest that the two meteorites are not paired. The CAI sizes and the abundance of melilite‐rich CAIs in MAC 88107 and 87300 suggests a genetic relationship to CO3 meteorites, but the CAIs in both have suffered a greater degree of aqueous alteration than is observed in CO meteorites. Aluminum‐rich melilite in CAIs from both meteorites generally contains excess 26Mg, presumably from the in situ decay of 26Al. Although well‐defined isochrons are not observed, the 26Mg excesses are consistent with initial 26Al/27Al ratios of approximately 3–5 times 10−5. An unusual hibonite‐bearing inclusion is isotopically heterogeneous, with two large and abutting hibonite crystals showing significant differences in their degrees of mass‐dependent fractionation of 25Mg/24Mg. The two crystals also show differences in their inferred initial 26Al/27Al ratios, 1 × 10−5 vs. ≤3 × 10−6.

Origin and multiple crystallization of the kamafugite-carbonatite association: the San Venanzo-Pian di Celle occurrence (Umbria, Italy)

AbstractThe Late Pleistocene kamafugite–carbonatite association at San Venanzo-Pian di Celle forms part of the Umbria-Latium Ultra-alkaline District (ULUD) of central Italy and, together with Toro-Ankole, SW Uganda and Mata de Corda, Brazil, represents one of three similar occurrences so far reported worldwide.Excellent field exposure and stratigraphic control prompted a study of the kamafugite–carbonatite suite and related phase interactions to understand the nature of the distinct mineral assemblages of the pyroclasts, compared to that of the lavas, the former containing essential potassium feldspar and aluminous diopside crystals, absent in the latter.The pyroclastic rocks represent a small amount of magma characterized by ubiquitous mantle xenocrysts and emplaced by early high-velocity eruptions. All the investigated specimens show a high Mg/(Mg+Fe2+) ratio (0.84–0.93) and high compatible elements (Ni+Cr&gt;1000 ppm). Lavas (venanzite, i.e. leucite melilitite) and a sill (uncompahgrite, i.e. melilitolite) represent final events in the volcanic sequence. They yielded a (Na+K)/Al ratio of c. 1.1 and are larnite-bearing in the CIPW norm. Glass from the lapilli is peralkaline, i.e. (Na+K)/Al&gt;2, and close to the lava in composition. Glass from melilitolite yielded CIPW Or and Hy and is strongly peralkaline, i.e. (Na+K)/Al = 5–6. The lapilli typically exhibit concentrically zoned structures which compound subliquidus venanzite phases, e.g. melilite, leucite, and kalsilite, with mantle xenolithic/xenocrystic debris and carbonatite phases. These lapilli represent a distinct variant of the venanzite liquid, mechanically fractionated and quenched by the diatremic process.Mantle-normalized HFSE for both lava and lapilli show typical extrusive-carbonatite patterns. Carbonatitic beds intercalated with the pyroclastic suite are distinct and typically consist of carbonates high in Sr, Ba and REE. Primary carbonate yielded C isotope compositions ranging from –5.0 to –6.0 δ13C‰, falling within the range of mantle compositions. Distinct differentiation trends of the venanzite magma and its derivatives were recognized, hinging on the coexistence of the silicate and carbonatite fractions. Potential sanidine crystallization trends are suggested, distinct from the venanzite→melilitolite trend, reported for Oldoinyo Lengai assemblages.Unusual aspects of the San Venanzo rock association, relative to similar rock types elsewhere, include the combination of a rare mantle source composition with a lithosphere about 80 km thick. A genetic model for the origin of the San Venanzo kamafugite–carbonatite association and related carbonate-silicate interactions is proposed and discussed. This may be relevant to the petrogenesis of similar rocks elsewhere, particularly in the light of the detailed data on the pyroclasts.

Subsilicic ferrian aluminian diopside from the Chelyabinsk coal basin (Southern Urals) – an unusual clinopyroxene

Subsilicic ferrian aluminian diopside from the Chelyabinsk coal basin (Southern Urals) – an unusual clinopyroxene

Site confirmation of Fe3+ in a synthetic ferrian aluminian diopside with an application of X-ray anomalous dispersion.

Crystals of ferrian aluminian diopside were synthesized and the structures were investigated by means of a single-crystal X-ray diffraction method in detail. EPMA gave the chemical formula of Ca1.00(Mg0.55Fe3+0.37Al0.08)(Si1.55Al0.45)O6 for the crystals as an average. Structure refinement indicated that about 9 % of Fe3+ ions are at T sites, giving the formula of Ca1.00(Mg0.55Fe3+0.34Al0.11)(Si1.55Al0.42Fe3+0.03)O6. Existence of Fe3+ at T sites was, however, not confirmed on a difference Fourier map synthesized by making use of anomalous dispersion effect at the Fe K absorption edge. The bond distances are reasonable for a ferrian aluminian diopside with a chemical composition found for the present crystals.

A new hyper-calcic amphibole with Ca at the A site; fluor-cannilloite from Pargas, Finland

Other| August 01, 1996 A new hyper-calcic amphibole with Ca at the A site; fluor-cannilloite from Pargas, Finland Frank C. Hawthorne; Frank C. Hawthorne CNR Centro di Studio per la Cristallochimica e la Cristallografia, Pavia, Italy Search for other works by this author on: GSW Google Scholar Roberta Oberti; Roberta Oberti Search for other works by this author on: GSW Google Scholar Luciano Ungaretti; Luciano Ungaretti Search for other works by this author on: GSW Google Scholar Joel D. Grice Joel D. Grice Search for other works by this author on: GSW Google Scholar American Mineralogist (1996) 81 (7-8): 995–1002. https://doi.org/10.2138/am-1996-7-821 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Frank C. Hawthorne, Roberta Oberti, Luciano Ungaretti, Joel D. Grice; A new hyper-calcic amphibole with Ca at the A site; fluor-cannilloite from Pargas, Finland. American Mineralogist 1996;; 81 (7-8): 995–1002. doi: https://doi.org/10.2138/am-1996-7-821 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Electron microprobe analysis of amphiboles from Pargas, Finland, shows up to 2.42 Ca apfu (atoms per formula unit), far in excess of the usual maximum value of 2.00 Ca apfu observed in amphiboles. The most Ca-rich composition is (K0.12Na0.35Ca0.52)(Ca1.92−Mn0.052+Fe0.032+)(Mg3.73Fe0.432+Ti0.02Al0.82)(Si5.63Al2.37)O22[(OH)0.46F1.54]⁠. Fluor-cannilloite, ideally CaCa2(Mg4Al)(Si5Al3)O22F2, is a new amphibole species in which Ca is dominant at the A site. Fluor-cannilloite occurs as isolated anhedral grains and small granular aggregates in a marble together with calcite, muscovite, anorthite, aluminous diopside, pyrope, and fluorite. It is grayish green with a grayish white streak, brittle, H = 6, Dmeas = 3.05 g/cm3, and shows perfect {110} cleavage. In plane-polarized light, it is pale greenish gray to almost colorless, rather cloudy and mottled in appearance, and is not pleochroic. Fluor-cannilloite is biaxial positive, α = 1.611(2), β = 1.616(2), γ = 1.633(2), 2V = 49(2)°, dispersion weak r > v. It is monoclinic, space group C2/m, a = 9.826(4), b = 17.906(9), c = 5.301(3) Å, β = 105.41(4)°, V = 899.2 Å3, Z = 2. The ten strongest X-ray diffraction lines in the powder pattern [d in Å(I)(hkl)] are 8.936(4)(020), 8.355(3)(110), 3.366(4)(131), 3.107(7)(310), 2.686(10)(151), 2.578(10)(061), 2.328(4)(351), 2.165(6)(171), 2.036(5)(202), 1.435(9)(4.10.1).The structures of fluor-cannilloite and another Ca-rich amphibole from Madagascar were refined to R indices of ∼1.5% using reflection intensities collected with MoKα X radiation. Site populations were assigned from the refined site-scattering values, considerations of mean bond lengths, and the unit formulas calculated from the electron microprobe analyses. Both the electron microprobe data and the site-scattering refinements show significant Ca (up to 0.52 apfu) together with Na and K at the A site. Both A2 and Am sites are occupied, with the A2 site having the higher electron density. Local bond-valence considerations indicate that Ca is equally partitioned between the A2 and Am sites, whereas K occupies Am and Na occupies A2. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.