Showing papers in "American Mineralogist in 1982"

Geothermometry, geobarometry and the Al2SiO5 triple point at Mt. Moosilauke, New Hampshire

Abstract: The distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the Acadian Orogeny to have been approximately those of the Al 2 SiO 5 invariant point, thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the Al 2 SiO 5 invariant point of Holdaway (1971). Four fluid-independent equilibria yield P-T estimates consistent with Holdaway (1971). Two fluid-dependent equilibria yield internally consistent but unrealistically high temperatures. Our data are consistent with the conclusions that: (1) only pyrope-grossular mixing in the quaternary garnet system is significantly non-ideal; and (2) the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point P-T conditions.--Modified journal abstract.

Thermodynamic calibration of geobarometers based on the assemblages garnet-plagioclase-orthopyroxene (clinopyroxene)-quartz

Abstract: Two mineralogic geobarometers based on the assemblage garnet-plagioclase-pyroxeneqvartz, common in granulite-grade quartzofeldspathic and basic lithologies, have been calibrated almost entirely from measured thermodynamic quantities, especially enthalpy of solution and heat capacity measurements For the continuous reaction: CaAl2Si2O6 + Mg2Si2O6: l/3Ca3Al2Si3O12 * 2/3Mg3Al2Si3Or2 + SiO2 (A) (plagioclase) (opx) the resulting geobarometric expression is: (quartz)

Sulfide saturation of basalt and andesite melts at high pressures and temperatures

Abstract: When the sulfur content of an Fe-bearing magma exceeds the saturation limit for the bulk composition, an immiscible iron sulfide melt fraction separates. For an understanding of the geochemistry of sulfur-bearing magmatic systems, more information is needed regarding the solubility of metal sulfide in silicate melt at its source and the solubility changes as a function of changing intensive and extensive variables. In the present investigation, the sulfur saturation surface is determined for the pressure range from 12.5 to 30 kbar and the temperature range from 1300 to 1460 C for three silicate melt compositions representing a range of SiO2 and FeO compositions.

A partisan review of Proterozoic anorthosites

Abstract: Most anorthosites of the massif type crystallized in the episode 1.7-1.2 Gyr, with a pronounced peak of the age distribution near 1.4 Gyr. They were emplaced anorogenically at depths as shallow as 7 km, where the ambient temperature of country rocks was probably less than 250'C. Depths of emplacement may have been as great as 25 km or more in rare cases; the greater depths of equilibration estimated from granulite facies metamorphism may be incorrectly interpreted as emplacement depths, but in any case they are demonstrably not required or characteristic of anorthosite emplacement. Penetrative deformation and metamorphism of anorthosites are post-emplacement accidents of the local geologic history, and are not directly caused by the presence of anorthosites. Granitic rocks (mangerite-charnockite suite) associated with anorthosite are in general later or contemporaneous products of crustal anatexis, with chemical and isotopic signatures distinct from the anorthosites and their residua. Such granitic rocks should not, therefore, be summed with the anorthositic rocks to obtain bulk compositions. The magmas that produced most anorthosites were dry, as shown by high-temperature mineralogy and anhydrous mineral assemblages in contact aureoles. Residua from their crystallization are ferrodiorites to ferrosyenites typical of closed-system fractionation. These residua were locally and frequently ejected into contemporaneously molten granite, where they formed pillows and cooled rapidly. The overall chemistry of anorthosites and residua is broadly tholeiitic and consistent with derivation from the mantle. Olivine-bearing magmas locally ranged from leucotroctolite (anorthosite) to later but coexisting picrite or melatroctolite in the same pluton, confirming a wide spectrum of magma types. A signal feature of troctolitic and noritic magmas is their low augite content, implying high content of spinel component. Large anorthosite complexes such as Nain and Harp Lake consist of many plutons representing repeated injections of separate magma batches with varying chemistry. The abundant true anorthosites, richer in plagioclase than magmas cosaturated with a mafic phase, must represent plagioclase enrichment by either mechanical or chemical processes or both. The role of kinetics in nucleation and solidification of such rocks may be centrally important. It is proposed that hyperfeldspathic (plagioclase-supersaturated) liquids were generated by quasi-isothermal extraction of mafic minerals from tholeiitic magma enroute to and at the site of emplacement, and that such a kinetic process was uniquely permitted in an environment of aborted continental rifting. Anorthositic rocks may have much to say about the episodic versus continuous geochemical evolution of the earth's mantle.

The crystal structure of lizardite 1T: hydrogen bonds and polytypism

Abstract: The occurence of lizardite 1T from Val Sissone, Italy, is reported. Electron microprobe analysis leads to the doubled unit cell content (Mgs .ssF e6.tsF e6.~oAlo.14) (Sh .66Alo. 34)0 1o.oo( 0 H)s.oo. The unit cell parameters are a = 5.332(3)A, c = 7.233(4)A, space group is P31m. The crystal structure has been refined, using 209 symmetry independent reflections, to R = 0.031. The refined model is not far from the idealized geometry of the serpentine layer. The ditrigonal distortion of the six-membered tetrahedral ring is small (a = 3.5°). No buckling of the brucite-like sheet is observed. The occurrence of both negative and positive a values in serpentine minerals is explained on the basis of stacking sequence and hydrogen bonds. Namely, the best hydrogen bond system is attained by rotation of the bridging oxygens belonging to the tetrahedral sheet. The direction of rotation depends on the way in which subsequent layers are stacked one upon the other. The substitution of trivalent atoms for magnesium and silicon leads to stronger hydrogen bonding between adjacent layers, thus promoting the formation of flatlayer structures and increasing thermal stability. Introduction symmetry, but Krstanovic (1968) refined his model in the space group Cm. Subsequently, Wicks and The well-known classification of the serpentine Whittaker (1975), in discussing Krstanovic's refineminerals was developed by Whittaker and Zussment, stated that lizardite IT \"is in fact orthorhommann (1956). The scheme is based on the recognibic and only pseudo-trigonal\". tion of cylindrical layers in chrysotile, corrugated Wicks and Whittaker (1975) and Krstanovic layers in antigorite, and flat layers in lizardite. A (1980) have discussed the distortions of both the recent review of the crystal structure of the serpentetrahedral and the octahedral sheets of a very pure tine minerals was given by Wicks and Whittaker lizardite 1T with limited substitutions for silicon or (1975). The most serious handicap to full undermagnesium. According to these authors, the comstanding of the serpentine structures is the low position of lizardite 1T from Radusa Mine results in degree of three-dimensional order present in these a large misfit between the tetrahedral and octaheminerals. For instance, the previous two-dimendral sheets, and produces shifts of the atoms away sional determinations of the crystal structure of from the ideal positions. In 'particular, they noted lizardite, by Rucklidge and Zussman (1965) and by buckling of the plane of the magnesium atoms and Krstanovic (1968), led to discrepancy factors of 18 various shifts, along [001], of the oxygen, silicon percent and 19 percent respectively, in spite of the and magnesium atoms. In this present paper, I fact the flat-layer lizardite structure would seem to report a more regular model for the crystal structure be the most promising for X-ray diffraction analyoflizardite 1Tfrom Val Sissone, Italy, that contains sis. significant aluminum and iron substitution. The Lizardite from Kennack Cove (Rucklidge and structure is not very different from the idealized Zussman, 1965) is composed of domains of 1T and geometry of the serpentine layer and was refined disordered 2H polytypes. Lizardite from Radusa using diffraction data obtained on euhedral crystals Mine (Krstanovic, 1968) is composed of the IT oflizardite IT. The different composition of the Val polytype. According to Rucklidge and Zussman Sissone lizardite IT, with its different structural (1965), the average crystal structure has trigonal constraints, limits comparison with the lizardite IT 0003-004X182/0506-0587$02.oo 587

Osumilite in the sapphirine-quartz terrane of Enderby Land, Antarctica; implications for osumilite petrogenesis in the granulite facies

Abstract: Osumilite is an important rock-forming mineral at l0 exposures in the Late Archean Napier complex of coastal Enderby Land (50-52'E), Antarctica. Mineral assemblages of low compositional variance (all with quartz-rplagioclase) are osumilite-garnet-sillimanite -r spinel, osumilite-sapphirine-sillimanite, osumilite-garnet-orthopyroxene-sillimanite, osumilite-orthopyroxene-biotite, and in a rock nearly free of iron (atomic Mg/(Mg+Fe) = 0.89) from Reference Peak (67'15'S, 50"29'E), osumilite-enstatite (EnerFse)-sillimanite. The Antarctic osumilite departs from the theoretical composition (K, Na) (Mg,Fe,Mn)zAlr (SiroAlto3o in that (Mg+Fe+Mn) ranges from2.20to2.39; A1,4.45 to 4.67; and Si, 10.05 to 10.30. These variations approximately obey the substitution (Mg+Mn+Fe) + Si : 2Al. Atomic Me/(Mg+Mn+Fe) ratio (X14j of Antarctic osumilite ranges from 0.79 to 0.97, and is greater than X1a, of associated cordierite and biotite. Antarctic osumilite-bearing have moderate to high Mg/Fe ratios (atomic Mg/(Mg+Fe) = 0.43 to 0.89) and are peraluminous. A petrogenetic grid in the system K2O-FeO-MgO-AlzOrSiO2 for quartz (present in all assemblages), osumilite, K-feldspar, garnet, sapphirine, cordierite, orthopyroxene, and sillimanite can be constructed given the constraint that the univariant reaction osumilite = cordierite * enstatite + K-feldspar + quartz in the iron-free subsystem intersects the stable portion of the univariant reaction in the MgO-Al2O3-SiO2 system: cordierite : enstatite + sillimanite -t qtartz. Pressure-temperature slopes of reactions involving osumilite but not cordierite are positive; slopes of reactions involving both osumilite and cordierite are negative, or in one case, parallel to the pressure axis. Osumilite is predicted to be stable in rocks of appropriate bulk composition at temperatures above 750'C and at total (lithostatic) pressures less than 8 or 9 kbar. M. Olesch and F. Seifert's recent experimental work and Olesch's calculations indicate that osumilite would be stable under hydrous conditions only when P11r6 = Prot.l < I kbar; at higher total pressures, H2O partial pressure must be much less than total pressure. Minimum temperatures for the appearance of osumilite-garnet and osumilite-sillimanite assemblages are in general higher than those needed for osumilitecordierite-orthopyroxene, and pressures of 5 or 6 kbar may be needed to stabilize osumilite-garnet or osumilite-sillimanite at geologically accessible temperatures. As the physical conditions proposed here for osumilite stability overlap the estimated conditions in many granulite-facies terranes, osumilite can be expected to occur at more localities than have been reported to date.

Thermodynamic studies of zeolites: analcime and dehydrated analcime

Abstract: Calorimetric measurements have been carried out on a pure speciment of analcime whose composition was Na/sub 0.96/Al/sub 0.96/Si/sub 2.04/O/sub 6/.H/sub 2/O and on the corresponding anhydride. The low-temperature heat capacity, standard enthalpy of formation (298.15 K), and high-temperature enthalpy increments have been determined by adiabatic, solution, and drop-calorimetric techniques, respectively. Thermodynamic functions have been calculated for analcime (to 600 K) and for dehydrated analcime (to 1000 K).

Crystal structure of a pink muscovite from Archer's Post, Kenya; implications for reverse pleochroism in dioctahedral micas

Abstract: The crystal structure of a reverse pleochroic muscovite containing both Fe3+ and Mn3* has been determined by standard single-crystal X-ray methods. The mica has a 2Mr polytype, space grou-p C 2lc. Cellconstants are a :5.1988A esd 0.0021, b = 9.02664 esd 0.0019, c : 20.1058A esd 0.Cf.44, I = 95JE2' esd 0.039, V = 938.724 esd 0.48. Average bond lengths in tetrahedral sites are 1.6464 and 1.639A, comparable to bond lengths in SiAl tetrahedra of other analyzed muscovites, but also compatible with minor site occupancy by Fe3*. Mean bond strengths and electron densities for the sites are also compatible with but do not require minor amounts of tetrahedral Fe3*. A pleochroic mechanism related to tetrahedral Fe3*, therefore, cannot be ruled out. Thermal vibration ellipsoids of atoms in the octatedral layer, however, are oriented with long axes perpendicular to the layer, which suggests the possibility that reverse pleochroism is due instead to an unusual configuration of d-orbitals for octahedrally-coordinated Fe3* or Mn3*.

Crystal structure of synthetic hafnon, HfSiO4, comparison with zircon and the actinide orthosilicates

Abstract: A crystal structure refineme-nt of a synthetic hafnon, HfSiO4, space group l4llamd with a: 6.5725(7)4, c = 59632(qA,Z: 4,D: 6.97 gmcm-3, produced positional parameters for oxygen ofy = 9.965t(13) and z: 0.1948(14) at R : 0.054. Hafnon has a zircon structure and the similar ionic radii of Hf (0.83A) and Zr (0.844) accounts for the interatomic distances and angles ofhafnon and zircon being identical within the stated errors, although hafnon has systematically smaller distances and corresponds to a zircon at 29.5 kbar pressure. Combining the hafnon, zircon and thorite structure refinements allows prediction of the oxygen positional parameters and bond lengths for the actinide (Pa, U, Np, Pu and Am) orthosilicates as well as possible extent of the solid solution among these zirconstructure silicates.

Orientation and effects of channel H 2 O and CO 2 in cordierite

Abstract: Channel CO2 and H2O has been re-introduced into a channel evacuated Mg-cordierite Ko.or Nao.o:(Mg1.e1Fe6.6eMno or)All e6Si5.s1O16 from White Well, Australia. At 600'C and pressures up to 6 kbar, a maximum of 3.13 wt.Vo CO2 and 2.6 wt.% H2O re-enter cordierite's channels. The H2O molecule orients preferentiallywithits H-H vectorparallelto c (opticorientation: c = X,b: Y,a: Z).Wirh increased H2O content, the refractive indices y and B increase more strongly than a whereas the as cell edge decreases, b0 perhaps increases slightly, and cs first increases and then levels off. The linear CO2 molecule orients chiefly parallel to cordierite's a-axis so that, as CO2 content increased, refractive index Tincreased more strongly than did aand B. As a result, 2V^ increased with CO2 content so as to exceed 90". Simultaneously, c6 increased, as decreased, and be remained constant. The distortion index A for these crystals changed with H2O and COz content.

Electronic and ionic polarizabilities of silicate minerals

Abstract: Molecular polarizabilities of silicate minerals are obtained using the Lorentz-Lorenz relation at optical frequencies and the Clausius-Mosotti relation at \"static\" frequencies. These polarizabilities are used to obtain a universal table of both electronic and static ion polarizabilities. Use ofthis set ofpolarizabilities shows that the additivity rule works rather well for complex silicates, i.e., the measured polarizability can be obtained from the appropriate sum of the ion polarizabilities in one formula unit. Therefore, the set of ion polarizabilities can be used in model calculations on the structure and bonding of silicates.

Plagioclase stability at elevated temperatures and water pressures

Abstract: The breakdown of plagioclase to zoisite, kyanite, quartz, and a more sodic plagioclase in the system NaAlSi/sub 3/O/sub 8/-CaAl/sub 2/Si/sub 2/O/sub 8/-H/sub 2/O has been investigated with reversed reactions at 8, 9, and 10 kbar. At these pressures all plagioclase compositions from approx.An/sub 40/ to An/sub 100/ break down along the same P-T curve as pure anorthite, which can be described by the equation P = -4590 + 20.4T(P = bars, T = /sup 0/C). The isobaric curves in the T-X section are thus represented by a horizontal line (constant temperature) between approx.An/sub 40/ and An/sub 100/. At compositions more sodic than approx.An/sub 40/ the curves dip rather sharply to lower temperatures. In the regions beneath the curves, the composition of sodic plagioclase along the down-dipping limb is in equilibrium with Zo + Ky + Qz. The remarkable behavior in the An/sub 40/-An/sub 100/ region suggests that under the hydrothermal conditions of this study, regions of ordered anorthite develop in the plagioclase and subsequently react with water as would independent crystals of An. Partial melting of pure An in the presence of water begins at 10.2 kbar and 725/sup 0/C. At 10.8 kbar a region of partial melt extends atmore » nearly the same temperature from An/sub 30/ to An/sub 100/. (JMT)« less

Mineralogy of mafic and Fe.Ti oxide-rich differentiates of the Marcy anorthosite massif, Adirondacks, New york

Abstract: Rocks enriched in mafic silicates, Fe-Ti oxides and apatite form a minor but ubiquitous facies of nearly all Proterozoic massif-type anorthosite complexes. In the Marcy massif of the Adirondack highlands, New York, the mafic rocks have two modes of occurrence: l) as conformable segregations interpreted as cumulate layers in the border zones, and 2) as dikes throughout the massif, interpreted as having crystallized from residual liquids extracted at varying stages during differentiation. Primary mineral compositions in these rocks are commonly preserved, despite the effects of subsolidus recrystallization in the high pressure granulite facies. In the mafic rock suite, primary compositions of mafic silicates reveal an iron enrichment trend which is broadly similar to that of basic layered intrusions, but suggestive of somewhat higher crystallization temperatures. Textural relationships suggest the following crystallization sequence: plagioclase, pigeonite + augite, hemo-ilmenite * magnetite, apatite. Fe-rich olivine replaced pigeonite in the lateststage residual liquids. The mineralogy and field relationships of these mafic rocks are consistent with their origin as diferentiates from the same melts which produced the anorthosites. This conclusion agrees with recent geochemical data that suggest an independent origi-n for the spatially associated mangerite-charnockite suite.

Use of exsolution lamellae in lunar clinopyroxenes as cooling rate speedometers: an experimental calibration

Abstract: Clinopyroxenes in Apollo 15 quartz-normative basalts (QNBs) are chemically complex recorders of thermal history. Texturally distinctive augite rims (Wo3sEna2) mantle the clinopyroxene phenocrysts and contain submicroscopic exsolution lamellae of pigeonite and augite near the (001) and (100) orientations. The size and morphologic variations of exsolution textures were characterized using the transmission electron microscope (TEM) in cooling rate experiments (cooled over the range 0.21o to 150"C/hr) on a synthetic QNB composition and in lunar samples 15597, 15499 and 15058. The size variation of (001) exsolution lamellae is used to estimate the sample's thermal history. The lamellae coarsen over the temperature interval 1100'-800'C, record cooling rate over this temperature range and may be used as cooling rate speedometers. Augite-pigeonite intergrowths form by spinodal decomposition, homogeneous nucleation, and heterogeneous nucleation. Coarsening of the lamellae produced in the cooling rate experiments may be described by the rate law: )r:)t'411113

The system albite–H2O–CO2: a model for melting and activities of water at high pressures

Abstract: The melting of albite in the presence of H2O-CO2 v?por has been determined in pistoncylinder apparatus from 5 to 25 kbar for mole fractions of HzO in the vapor (Xfir6) from 1.0 to 0.0. Albite in the presence of CO2-rich vapor melts as much as 150-300'C lower than indicated by previous theoretical and experimental studies. The albite-CO2 melting curve is indistinguishable from the vapor-absent melting curve up to l5 kbar, but it is significantly lower above 15 kbar as a result of a substantial increase in the Solubility of COz in the liquid. Calculated activity coefficients (y) for water in H2O-CO2 vapor in the range 7001000"C, 5-15 kbar are everywhere greater than unity and increase isobarically and isothermally toward COz-rich compositions. For Xfir6 < 0.3 calculated lffro are significantly greater than those predicted by the modified Redlich-Kwong equation.

Structural hydroxyl in chalcedony (type B quartz)

Abstract: Chalcedony is shown by infrared and X-ray study to contain (OH) in structural sites in addition to several types of non-structural water. (OH) varies zonally; the (OH)-rich zones are more rapidly etched, have lower X-ray reflection angles, lower indices of refraction, and whiten on heating to 550-600 degrees C. Distinctive infrared absorption spectrum in the 3200 cm (super -1) to 3600 cm (super -1) region (type B); different spectrum in this region is afforded by natural quartz crystals formed at higher temperatures (type A). The structural (OH) is housed by different mechanisms in these two types of quartz, apparently depending on the structural role and availability of Al.--Modified journal abstract.

Suessite, Fe 3 Si; a new mineral in the North Haig ureilite

Abstract: The North Haig olivine pigeonite achondrite (ureilite) is a polymict breccia consisting of major olivine, low-Ca pyroxene and an intergranular carbonaceous matrix. Olivine and low-Ca pyroxene vary widely in composition, covering the ranges observed in all known ureilites. Minor granular enstatite clasts with diopside exsolution blebs, dkin to enstatite achondrites, were also observed. Native metal in ureilites is normally kamacite of variable Ni content, in some cases with up to ZVo Si in solid solution. However, kamacite with trace amounts of Si is extremely rare in North Haig, only a few l-2 p.m grains within silicates were observed. Instead, the common metallic phase is approximately Fe3Si, a new mineral which we have named suessite in honor of Professor Hans E. Suess. Suessite occurs as minor anhedral vein fillings in interstitial cracks, in silicates, and in the intergranular carbonaceous material and ranges in size from 1 pm blebs to elongated grains about 30 x 150 pm in size. Suessite is cream white in reflected light, isotropic, ferromagnetic, and shows no cleavage. Reflectance in percent (determined by G. A. Desborough) at the 4 standard wavelengths of 470, 546, 589 and 650 nm for 2 grains is 48.5(5), 51.6(3), 53.5(7), 50(2), and 49.7(5\, 53.4(4), 54.5(6), 52(l), respectively. Analyses (by EMX) indicate presence of dominating low-Ni and less common high-Ni varieties of suessite (in wt.Vo, mean in parentheses): Fe 84.7, 83.1 (8a.2); Ni 1.6, a.5 Q.5); Co 0.21, 0.27 (0.23); Cr 0.10, 0.04 (0.08); Si 15.3, 13.7 Oa.7); P 0.06, 0.17 (0.10). Thus, suessite is (Fe, Ni, Co, Cr)z sa_t M (Si, P)f .0, mean(Fe, Ni, Co, Cr)2 e6(Si, P)r.0, very close to Fe3Si. X-ray powder diffraction shows that suessite possesses a similar structure to alpha-Fe (kamacite) and the solid solution alloy (Fe3Si),, in displaying three lines (relative intensities in parentheses): 2.005(10), 1.42(l),1.160(3) (in A). rne calculated cell size is 2.841t0.0024 N : 22.%Ar. Thus, suessite is the Si-rich end member of the cr solid solution region of the Fe-Si phase diagram with composition close to Fe3Si. Silicates, particularly olivine, in ureilites have core compositions of Fo.to-gz and thin (<100 p,m) rims of essentially Folso formed by reduction and reaction with the carbonaceous matrix material. We suggest that Si and Fe liberated in this reduction process formed suessite, possibly also by reaction with preexisting kamacite.

Alteration of spodumene, montebrasite and lithiophilite in pegmatites of the White Picacho District, Arizona

Abstract: The crystallization sequence and metasomatic alteration of spodumene (LiAlSizOe), montebrasite (LiAIPO4(OH,F)), and lithiophilite (Li(Mn,Fe)PO+) are described for nine zoned lithium pegmatites in the White Picacho district, Arizona. The observed crystallization trends suggest a progressive increase in the activities of lithium species (spodumene follows microcline as the principal alkali aluminosilicate), as well as an increase in the activities of the acidic volatiles phosphorus and fluorine (montebrasite succeeds spodumene as the stable primary lithium phase). Much of the lithiophilite occurs with columbite, apatite, beryl, zircon, and tourmaline in cleavelandite complexes that formed in part at the expense of quartz-spodumene pegmatite. Fracture-controlled pseudomorphic alteration of the primary lithium minerals is widespread and apparently is the result of subsolidus reactions with residual pegmatitic fluids. Spodumene has been replaced by eucryptite, albite, and micas. Alteration products of montebrasite include low-fluorine secondary montebrasite, crandallite (tentative), hydroxylapatite, muscovite, brazilianite, augelite (tentative), scorzalite, kulanite, wyllieite, and carbonate-apatite. Secondary phases identified in altered lithiophilite include hureaulite, triploidite, eosphorite, robertsite, fillowite, wyllieite, dickinsonite, fairfieldite, Mn-chlorapatite, and rhodochrosite. Initial subsolidus metasomatism of the lithium minerals took place in an alkaline environment, as evidenced by albitization of spodumene and calcium metasomatism of the phosphates. The formation of secondary micas in spodumene, montebrasite, tourmaline, and much feldspar reflects a change from alkaline to relatively acidic postmagmatic fluids, as (K+H)-metasomatism produced greisen-like or sericitic alteration. The abundance of minerals containing Li, Be, Mn, Nb, Ta, and Bi indicate that these pegmatites originated from a highly differentiated granitic source. These pegmatites were not fluorine-rich, as evidenced by the low fluorine contents of primary and secondary montebrasite, by the formation of OH- and Cl-apatites, and by the absence of topaz and the rarity of lepidolite, triplite, and fluorite.

The thermodynamic properties of fluor'topaz

Abstract: The standard thermodynamic properties of fluor-topaz, AlzSiOnFz, have been calculated from low- and high-temperature heat-capacity measurements and from high-temperature, oxide-melt calorimetry. Fluor-topaz (from Topaz Mountain, Thomas Range, Utah) containing 0.04 wt. percent water was used in all the experiments. Adiabatic calorimetry performed from 10.6 to 379.2 K gives Si9E - Si of 105.4 * 0.2 J/mol'K. Combined heat capacities determined by adiabatic calorimetry (200-380 K) and differential scanning calorimetry (340-800 K) were fit to the following polynomial (equation valid 200-1,000 K): c; (ymol.K) = 471.41- 0.08165r + l.2695xlO6T-2 - 5485.510'5 eO.1%).