Albite Crystals Research Articles

Oxygen diffusion studies. I. A preliminary ion microprobe investigation of oxygen diffusion in some rock-forming minerals

AbstractThe self diffusion of oxygen has been studied in prepared natural crystals of albite, grossular garnet, quartz, and ruffle by isotope exchange with hydrothermal water enriched in 18O, and subsequent analysis by ion microprobe. Measured oxygen diffusion coefficients (D) in quartz (‖c) may be described by D = 1.08 × 10−11 exp(−31.5 kcal/RT) cm2s−1 at 600−750°C and 1 kbar water pressure. For grossular, D = 2.5 × 10−16 cm2s−1 at 1050°C and 8 kbar, and D = 4.8 × 10−17 cm2s−1 at 850 °C and 2 kbar. All ruffle crystals exhibited variable amounts of corrosion, and an approximate diffusion coefficient of D(‖c) = 3.16 × 10−15 cm2s−1 cm2s−1 was obtained at 1050 °C and 1 kbar. Oxygen diffusion coefficients in albite, perpendicular to (001) faces, have been determined as a function of pressure at 600 °C Between 0.5 and 8.0 kbar pressure no systematic variation in the results was observed and most of the data may be described by D = 4.1 (±0.5) × 10−15 cm2s−1. Slow oxygen diffusion rates in quartz and garnet suggest that these minerals should have high ‘closure temperatures’ for oxygen exchange, and may provide reliable oxygen isotope exchange geothermometers.

On the internal nucleation of melting

Crystals of quartz have been superheated by some 450°C and crystals of albite by some 185°C above their respective melting points. In all cases, melting took place by the nucleation of liquid at the external surfaces (and internal boundaries as well in the case of albite). No evidence for the internal nucleation of liquid was found at any superheat for either material. The results of quartz indicate an exceptionallu large barrier to the internal nucleation of liquid. It is suggested that this large nucleation barrier is associated with the strain energy of forming a liquid nucleus within the crystalline phase. It is also indicated that the nucleation of liquid at the external surfaces of crystals at negligible superheats suggests that the free surfaces of liquids do not per se serve as preferred nucleating sites for crystallization — and that the crystal nucleation often observed at external surfaces or internal surfaces is in fact associated with condensed second-phase impurities.

A 1,220�60 M.Y. Rb-Sr isochron age representing a Taylor-convection caused recrystallization event in a granitic rock suite

In the Tisselskog area (N. Dalsland), in the eastern, external part of the Grenvillian belt in N. Europe, two formations of granitic rocks form the basement for the basal sediments of the Grenvillian, Dalslandian Group. Basement and cover went through a low grade regional metamorphism at 1,030±40 m.y. (2σ) ago. The granitic rocks are strongly recrystallized, but have preserved their granitic texture. Most magmatic crystals are pseudomorphed by a suite of metamorphic crystals of quartz, albite, chlorite, white mica, epidote, titanite, hematite, pyrite and carbonate. It is remarkable that these rocks with a perfect magmatic appearance have lost so much of their magmatic mineralogy. The older of the two intrusions, the Ballsjon Granodiorite Formation, yields a 7 point, 1,220±60 m. y. Rb-Sr isochron (initial Sr isotope ratio=0.7048±0.0004, λ87Rb=l.42×10−11·y−1). This age is interpreted as representing the pervasive recrystallization in the rocks, which was induced by a hydrothermal convective circulation system — a Taylor convection — set up by the intrusion itself or by the younger Tisselskog Leucogranite Formation which intrudes it. In dating a phase of pervasive hydrothermal resetting by whole rock Rb-Sr dating one should try to strike a balance between maximal Rb/Sr variation and maximal similarity in the starting mineralogy in the rock samples, the latter aiming at geochemical coherence during the hydrothermal alteration.

Influences of kinetics and mechanism in metamorphism: a study of albite crystallization

The kinetics and mechanisms of reactions: 1. (I) Analcite + Quartz = Albite + H 2O. 2. (II) Jadeite + Quartz = Albite. have been studied at 300–500°C. P(fluid) = 1 kbar, in aqueous solutions 0.1 M NaCl and 0.05 M Na 2Si 2O 5 (NaDS). Albite is the only phase to form, with the exception that at 300°C reaction II in NaCl forms metastable analcite with an Al 2O 3 SiO 2 ratio of 1:6. All reaction occurs by solution-precipitation mechanisms. The effects of the two solutions are opposed; reaction I in NaDS solution is faster than in NaCl, whereas reaction II proceeds more quickly in NaCl. The kinetics of reaction I can be substantially described by: X Ab = K · t 3 2 (X Ab = mole fraction of product albite, t = time of reaction and K is a rate constant). Reaction II appears to behave according to: X Ab = K' · t 1 2 . In both reactions nucleation appears to be kinetically negligible. Oxygen isotope fractionation between albite and water at 350–500°C is described by: 1000 In α Ab- H 2 O = 2.81 ± 0.11 × 10 6 T −2 −3.50 ± 0.23. The temperature dependencies of the rate constants for reaction I can be described by the functions: K NaCl = 1.2 × 10 11 ± 50 · exp(−44.5 ± 5.6 kcal/ RT) K NaDs = 7.1 × 10 17 ± 10 · exp(−60.8 ± 3.0 kcal/ RT). Basic problems in petrological applications of these rate equations are differing rate controlling mechanisms in natural and experimental situations and the complexities of metamorphic kinetic controls. Extrapolations of the Arrhenius equations suggest that the kinetics of reaction I would not perturb its occurrence at equilibrium in regional (burial) metamorphism [except, perhaps, when P(H 2O) < P(load)]. However, in contact metamorphism ‘overshooting’ of equilibrium may occur, leading to partial reaction in outermost zones of metamorphism and attenuation of thermal aureoles.

Late Precambrian ash-flow tuffs and associated rocks of the Harbour Main Group near Colliers, eastern Newfoundland: chemistry and magmatic affinities

The Colliers Peninsula, a typical area in the western part of the Harbour Main Group in eastern Newfoundland, is underlain by three steeply-dipping sequences of ash-flow tuffs 250–500 m thick, separated by clastic sediments, conformably overlain by subaerial mafic flows and cut by small bodies of high-level intrusive rocks rich in plagioclase phenocrysts. All rocks are of low metamorphic grade.The two lower pyroclastic sequences have a bulk composition of rhyolite and alkali rhyolite; they contain phenocrysts of albite, quartz, and biotite. Na/K ratios are highly variable; the albite crystals may be pseudomorphous after anorthociase. The upper sequence, rhyodacitic in bulk composition, has lower Si and higher Na; it lacks quartz and biotite phenocrysts but contains small amounts of calcic augite and altered olivine. The mafic flows (50% SiO2) show high Al and alkalies and low Ca and Ti. The porphyritic intrusives have 60–65% SiO2, but their bulk chemistry is otherwise similar to that of the ash-flow tuffs.The present composition of the rocks reflects complex chemical adjustments, both contemporaneous with and subsequent to the magmatic event. However, mineralogical and chemical data and trends considered to be a part of the original magmatic heritage are consistent with suggestions that the western (probably lower) part of the Harbour Main volcanic pile was formed in a continental, extensional tectonic environment.

A trachyte dike in the northern part of Shidara area, Aichi Prefecture, Japan.

In the northern part of Shidara area, where acid Miocene volcanics are widely distributed, numerous alkali basalt dikes and sheets occur and some of them were studied by Kuno (1960). A trachyte dike also occur in the area and it is most alkaline among the rocks of the area. The trachyte consists of phenocrysts of ferrohedenbergite rimmed to sodic ferrohedenbergite, fayalite, arfvedsonite, plagioclase and alkali feldspar. Groundmass minerals are alkali feldspar sodic ferrohedenbergite, aenimgatite and titanomagnetite. The trachyte includes small xenoliths, which may have been trachybasalt as variolitic and labradorite core of plagioclase phenocryst are preserved. The xenoliths consist of titanaugite rimmed to aegirinaugite, ferroaugite, aegirinaugite, arfvedsonite, plagioclase, aenigmatite and titanomagnetite. Enrichment of acmite molecules in pyroxenes such as sodic ferrohedenbergite and aegirinaugite and crystallization of arfvedsonite, albite, alkali feldspar and aenigmatite may be due to reaction between trachyte including xenoliths and alkali-rich residual fluid at the latest stage. Crystallization trend of pyroxenes of the trachyte is different from that of the xenoliths. Trend of the former is ferrohedenbergite-sodic ferrohedenbergite and that of the latter is titanaugite-aegirinaugite. However, in the latest stage, it seems that sodic ferrohedenbergite and aegirinaugite have crystallized on similar condition which nearly corresponds to “no oxide field” proposed by Nicholls and Carmichael (1968).

Ascent and Crystallization of Albite and Granitic Melts Saturated with $$H_{2}O$$

Crystallization of a magma can occur adiabatically if dissolved water is removed from the melt by a reduction in pressure. Thermodynamic calculation of the adiabatic ascent of a parcel of water-saturated $$NaAlSi_{3}O_{8}-H_{2}O$$ magma along the saturated liquidus for albite-$$H_{2}O$$ yields a series of curves for various initial concentrations of $$H_{2}O$$ which describe the crystallization with decrease in pressure. For example, an $$NaAlSi_{3}O_{8}-H_{2}O$$ magma initially saturated at 3 kb with 7.7 weight percent water will be about 50% crystallized at pressure of 1.5 kb, and will contain a residual liquid with 5.4 wt.% water. It appears likely that granitic magmas with more than 15% of water initially cannot get out of the lower crust, and that granitic magmas with more that 5% initial water can only reach the surface by means of irreversible explosive processes.

Franciscan blueschist-facies metaconglomerate, Diablo Range, California

Certain Franciscan conglomerate units are shown to be metaconglomerate and to exhibit selective blueschist-facies metamorphism of various constituents. Petrographic and x-ray studies were made on pebbles and matrix of 18 Franciscan conglomerate units forming blocks in melanges and lenses in stratiform bodies of graywacke in the vicinities of Mount Hamilton and Pacheco Pass. The conglomerate ranges from little-deformed varieties (textural grade 1) to tectonite with pronounced secondary planar structures (textural grade 2). Significant minerals in conglomerate of textural grade 1 are quartz + albite ± lawsonite ± minor glaucophane + CaCO 3 , and those of textural grade 2 are lawsonite + glaucophane + quartz ± jadeitic pyroxene ± albite ± aragonite. Thus the most intense metamorphism is empirically associated with internal deformation; however, the converse is not invariably true. Lawsonite in granitic clasts favors feldspar, but its abundance varies within single clasts, from clast to clast, and between adjacent conglomerate units; it commonly forms crystallographically oriented prisms in albite and is locally concentrated near the margins of albite crystals. Glaucophane, which is scarce in conglomerate of textural grade 1, is locally concentrated as rinds in some clasts of fine-grained basalt or it forms rare fibrous prisms in granitic clasts. In rocks of textural grade 2, it commonly forms beards on green amphibole in the matrix and in granitic clasts and completely replaces some mafic clasts. Jadeitic pyroxene replaces albite in conglomerate of textural grade 2 and is concentrated in the outer parts of certain clasts. Carbonate, commonly aragonite, shows crosscutting relations with lawsonite, glaucophane, or jadeitic pyroxene. Paragenetic relations between lawsonite and glaucophane are equivocal, but probably both minerals formed earlier than jadeitic pyroxene. Albite is apparently the only feldspar in the metaconglomerate units. The chemistry of granitic clasts is reflected in their metamorphosed mineral assemblages. They are deficient in potassium and enriched in sodium relative to average granite of similar silica content. The mineral assemblages of the metaconglomerate are consistent with those reported from nearby metagraywacke units, although there is generally no structural continuity with the metagraywacke. Petrographic features indicate postdepositional blueschist-facies metamorphism of the conglomerate units and demonstrate the presence of a fluid phase during metamorphism.

Late Precambrian ignimbrites on the Avalon Peninsula, Newfoundland

The predominantly volcanic Harbour Main Group of Late Precambrian age, forming a broad northerly trending belt in the central part of the Avalon Peninsula of Newfoundland, includes some well-developed ignimbrites. The ignimbrite sequence, best exposed in the western part of the volcanic belt, consists of ash-flow tuffs intercalated with tuff–breccias of various origins and minor volcanigenic sediments. Some of the ignimbrite sheets are densely welded, with distinct eutaxitic structures. Although the original glass is recrystallized, shard outlines are perfectly preserved and fragments of obsidian and perlite can be recognized; albite crystals are abundant, and quartz, augite, and biotite are present locally. The ignimbrites have been folded, faulted, and are now almost vertical. In composition, they range from rhyolites to dacites and are distinctly sodic.It is suggested that the ignimbrites may be derived from the gas-charged upper part of a granitic magma intruded into a pre-existing part of the Harbour Main volcanic pile; the lower, gas-poor part of the magma may have formed the present discordant "Holyrood batholith" of the Avalon Peninsula.

A high-temperature X-ray study of the equilibrium forms of albite

SummaryComplete lattice parameters have been determined at a series of temperatures up to 950 °C using a furnace on a powder diffractometer for six synthetic supposed equilibrium albites, a nonequilibrium albite, two natural albites, and a heat-treated natural albite. The supposed equilibrium albites were prepared hydrothermally by MacKenzie (1957) for long periods of time and reached or nearly reached a state of no further change at their temperatures of synthesis between 500 and 1000 °C. A crystal of natural albite and three crystals of heat-treated natural albite were studied by high-temperature, single-crystal methods on a Buerger precession camera up to 1000 °C for comparison.The lattice angles for each albite decrease smoothly with increasing temperature; the a-axis and the volume increase smoothly with increasing temperature. The rates of change increase with increasing temperature. The c and in some cases the b-axes appear to decrease initially in the range 25–300 °C and then subsequently increase. The thermal dilatation is highly anisotropic—the change in a is about twice that in b and about six times that in c over the whole range 25–850 °C. The effect of a temperature rise on the lattice parameters of the albites is very similar to the effect of the substitution of potassium on the room-temperature parameters.Plots of α* against γ* for each albite at a sequence of temperatures up to 950 °C fall on nearly straight parallel lines, all albites becoming less oblique (triclinic) with increasing temperature. Of the equilibrium albites, only the one synthesized at 1000°C becomes monoclinic below the melting point. The ratio d010/d001 or c*/b* is a measure of order in the albites and does not vary with temperature. The similar behaviours of this ratio and of other lattice parameters as a function of the temperature of synthesis confirms the two-step ordering process in albite.

Melting Relationships in the System $$NaAlSi_{3}O_{8}-NaF-H_{2}O$$ to 4 Kilobars Pressure

The phase relationships in the systems $$NaF-H_{2}O$$ and $$NaAlSi_{3}O_{8}-NaF-H_{2}O$$ were determined between 600° and 900° C. at pressures up to 4 kb., and those in the anhydrous system $$NaAlSi_{3}O_{8}-NaF$$ were determined at 1 atm. The phases encountered were albite, villiaumite (NaF), liquid, and vapor. The liquid quenches to a glass containing skeletal NaF crystals. Primary villiaumite is readily distinguished from "quench" NaF. Albite crystals coexisting with liquid are several times larger than subsolidus crystals. The binary reaction villiaumite + vapor $$\rightleftharpoons$$ liquid occurs at $$860^\circ \pm 7^\circ C$$. at 1 kb., and the binary reaction albite + villiaumite $$\rightleftharpoons$$ liquid occurs at $$860^\circ \pm 5^\circ C$$. at 1 atm. The beginning of melting in the ternary system is the reaction albite + villiaumite + vapor $$\rightleftharpoons$$ liquid; this occurs at $$753^\circ \pm 5^\circ C$$. at 0.5 kb., at $$688^\circ \pm 5^\circ C$$. at 1 kb., at $$640^\circ \pm 5^\circ C$$. at 2 kb., at $$630^\circ \pm 5^\circ C$$. at 3 kb., and at $$600^\circ \pm 5^\circ C$$. at 4 kb. The composition of the univariant liquid in the system $$NaF-H_{2}O$$ at 1 kb. is approximately 80 wt. per cent NaF and 20 wt. per cent $$H_{2}O$$; the composition of the univariant liquid in the anhydrous system is approximately 84 wt. per cent $$NaAlSi_{3}O_{8}$$ and 16 wt. per cent NaF. The composition of the univariant liquid in the ternary system varies with pressure. At 1 kb. the composition expressed in terms of the anhydrous components is approximately 86 wt. per cent $$NaAlSi_{3}O_{8}$$ and 14 wt. per cent NaF, and the water content is about 30 wt. per cent; at 4 kb. it is approximately 75 wt. per cent $$NaAlSi_{3}O_{8}$$ and 25 wt. per cent NaF, and with a water content of about 45 wt. per cent. Critical conditions are probably reached at a pressure not far above 4 kb. The solubility of the solids in the vapor phase at 4 kb. is about 40 wt. per cent. These results indicate that small variations in NaF content of a silicate magma can produce large variations in the water content of residual magmas and large variations in the amount of water required to saturate the magma. NaF causes residual magmas to persist to significantly lower temperatures than the final consolidation temperature if $$H_{2}O$$ were the only dissolved volatile component.

Experimental Investigation of Silicate Systems Containing Two Volatile Components; Part 2, the Effects of NH 3 and HF, in Addition to H 2 O on the Melting Temperatures of Albite and Granite

Addition of NH 3 to water-albite and water-granite mixtures at constant pressure raises the melting temperatures of albite and granite, whereas addition of HF to these mixtures causes marked lowering of melting temperatures. Results obtained at 2,750 bars pressure for charges containing 1:1 weight ratio of silicate to total volatiles are presented as perspective TX projections from within isobaric prisms onto the volatile faces of the prisms. In the presence of H 2 O alone at 2,750 bars pressure, albite melts between 795 degrees C. and 810 degrees C., and granite begins to melt at 670 degrees C.; in the presence of 8.2 weight percent NH 3 solution, the melting interval of albite is 805 degrees C. to 825 degrees C., and granite begins to melt at 690 degrees C.; in the presence of 8 weight percent HF solution, the melting interval of albite is 610 degrees C. to 685 degrees C., and granite begins to melt at 595 degrees C. No chemical reaction was detected in systems containing NH 3 , but considerable reaction occurs with HF. With increasing HF concentration in the system NaAlSi 3 O 8 -H 2 O-HF, quartz becomes a stable phase and the system is no longer ternary. In the presence of HF solutions, albite crystals grow much larger than in the presence of H 2 O alone.

Observations on Heat-Treated Authigenic Microcline and Albite Crystals

As part of a general study of authigenic feldspars, microcline and albite crystals of authigenic origin were heat-treated at temperatures near the melting point of albite. Within 28 days the microcline crystals were converted by a diffusive disordering transformation to sanidine. Untwinned albite cleavage fragments transformed to analbite within 10 days, and a measurable change in the reciprocal lattice angle γ was observed in one day. The transformation from low-temperature albite to analbite is gradational in character, and it is evident that the crystals pass through all intermediate states; it is thus similar to the micro-cline-sanidine transformation. During the heating period the albite crystals became mosaic and produced smeared X-ray reflections. The mosaic structure appears to be related to the formation of the unquenchable monoclinic form of NaAlSi₃O₈, the existence of which is deduced from fine albite and pericline twinning. After the crystals had completely transformed to monoclinic NaAlSi₃O₈ ...

Authigenic Albite in the Green River Oil Shales

ABSTRACT Very small crystals of authigenic albite have been found in those layers of the Green River formation with the highest content of organic matter. The nature of the Green River sediments clearly implies a low temperature of formation for the feldspar and suggests a relation between the organic matter and the authigenic mineral.

Authigenic Albite from the Lowville Limestone at Bellefonte, Pennsylvania

ABSTRACT Insoluble residues, obtained from the Lowville limestone at Bellefonte, Pa., show appreciable quantities of authigenic albite of unusual purity. The mineral occurs as twinned idiomorphic crystals, the largest of which are about one-fourth millimeter along the major diameter. Inclusions of small rhombs and granules of calcite are commonly observed in the albite crystals. The authigenic character of the albite is suggested by the unusual chemical composition, idiomorphic habit, the dearth of associated clastic materials, and the manner of distribution in the limestone. The crystals do not appear to be confined to special horizons, nor are they related genetically to fracture zones which may be considered avenues of circulation for hydrothermal solutions. The enclosing rock shows no trac of metasomatic change or heat effects of any kind, nor do the crystals appear to show replacement features, but rather they suggest formation in the calcareous muds of the sea floor during deposition and compaction of the sediment. Complete chemical analyses of the feldspar collected at random from several different parts of the Lowville rock show no potash but an unusually high soda content.

The Petrology of the Warren House Series, Malvern

THE Warren House Series consists of lavas which belong to a sodic suite, being rhyolites, keratophyres, and spilites. The rhyolites have a fine-grained micrographic groundmass, and some contain phenocrysts of quartz, orthoclase, anorthoclase, and plagioclase felspar. Epidotization of the rocks has occurred, but it is the felspathic and femic constituents of the groundmass which have suffered alteration and not the felspar phenocrysts, the action not being intense enough to affect the latter. The keratophyres consist essentially of small lath-shaped albite crystals which give a trachytic texture to the rock. The spilites are more basic, vesicular, and variolitic or sub-ophitic in texture, while some of them show pillowstructure in the field. The keratophyres and the spilites also exhibit varying degrees of epidotization. Pyroclastic rocks are not very common, but a few interesting varieties have been noted. Intrusions of dolerite occur within the lavas. One type is an ophitic dolerite, which when fresh probably contained olivine. Another type is now an epidiorite. Both these types have been epidotized, the epidiorite to such an extent that it passes into an epidote-uralite rock in places.

On crystals of Albite from Alp Rischuna, and pericline twins from La Fibbia, Switzerland

The Cambridge Museum recently acquired a number of albite specimens from Alp Rischuna, near Yals Platz in Switzerland. Many of the crystals had good faces, so that measurement of the angles seemed likely to give trustworthy crystal-elements.

II. On the constituent minerals of the granites of scotland, a compared with those of donegal

During the past summer (1869) I completed my investigation of the constituent minerals of the Scotch Granites, and secured specimens, from the analysis of which I obtained the following results:— No. 1. Stirling Hill, Peterhead. Occurs in an eruptive Granite, in veins, in well-developed reddish-pink opaque crystals, encrusted with crystals of Albite. No. 2. Rubislaw, Aberdeen. Large beautiful reddish-pink opaque crystals in veins, associated with white Mica. The Granite of Rubislaw is of metamorphic origin, and different in character from the erupitve Granite of Peterhead. No Albite has been found in it.