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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 73 records · Page 4Linked to original sources
USGS2009

Biomineralization associated with microbial reduction of Fe 3+ and oxidation of Fe 2+ in solid minerals

Iron-reducing and oxidizing microorganisms gain energy through reduction or oxidation of iron, and by doing so play an important role in the geochemical cycling of iron. This study was undertaken to investigate mineral transformations associated with microbial reduction of Fe 3+ and oxidation of Fe 2+ in solid minerals. A fluid sample from the 2450 m depth of the Chinese Continental Scientific Drilling project was collected, and Fe 3+ -reducing and Fe 2+ -oxidizing microorganisms were enriched. The enrichment cultures displayed reduction of Fe 3+ in nontronite and ferric citrate, and oxidation of Fe 2+ in vivianite, siderite, and monosulfide (FeS). Additional experiments verified that the iron reduction and oxidation was biological. Oxidation of FeS resulted in the formation of goethite, lepidocrocite, and ferrihydrite as products. Although our molecular microbiological analyses detected Thermoan-aerobacter ethanolicus as a predominant organism in the enrichment culture, Fe 3+ reduction and Fe 2+ oxidation may be accomplished by a consortia of organisms. Our results have important environmental and ecological implications for iron redox cycling in solid minerals in natural environments, where iron mineral transformations may be related to the mobility and solubility of inorganic and organic contaminants.

American Mineralogist↗
USGS2009

Steric hindrance and the enhanced stability of light rare-earth elements in hydrothermal fluids

A series of X-ray absorption spectroscopy (XAS) experiments were made to determine the structure and stability of aqueous REE (La, Nd, Gd, and Yb) chloride complexes to 500 ??C and 520 MPa. The REE 3+ ions exhibit inner-sphere chloroaqua complexation with a steady increase of chloride coordination with increasing temperature in the 150 to 500 ??C range. Furthermore, the degree of chloride coordination of REE 3+ inner-sphere chloroaqua complexes decreases significantly from light to heavy REE. These results indicate that steric hindrance drives the reduction of chloride coordination of REE 3+ inner-sphere chloroaqua complexes from light to heavy REE. This results in greater stability and preferential transport of light REE 3+ over heavy REE 3+ ions in saline hydrothermal fluids. Accordingly, the preferential mobility of light REE directly influences the relative abundance of REE in rocks and minerals and thus needs to be considered in geochemical modeling of petrogenetic and ore-forming processes affected by chloride-bearing hydrothermal fluids.

American Mineralogist↗
USGS2009

Mineralogy of mine waste at the Vermont Asbestos Group mine, Belvidere Mountain, Vermont

Samples from the surfaces of waste piles at the Vermont Asbestos Group mine in northern Vermont were studied to determine their mineralogy, particularly the presence and morphology of amphiboles. Analyses included powder X-ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and Raman spectroscopy. Minerals identified by XRD were serpentine-group minerals, magnetite, chlorite, quartz, olivine, pyroxene, and brucite; locally, mica and carbonates were also present. Raman spectroscopy distinguished antigorite and chrysotile, which could not be differentiated using XRD. Long-count, short-range XRD scans of the (110) amphibole peak showed trace amounts of amphibole in most samples. Examination of amphiboles in tailings by optical microscopy, SEM, and EPMA revealed non-fibrous amphiboles compositionally classified as edenite, magnesiohornblende, magnesiokatophorite, and pargasite. No fibrous amphibole was found in the tailings, although fibrous tremolite was identified in a sample of host rock. Knowledge of the mineralogy at the site may lead to better understanding of potential implications for human health and aid in designing a remediation plan.

American Mineralogist↗
USGS2010

Monoclinic tridymite in clast-rich impact melt rock from the Chesapeake Bay impact structure

X-ray diffraction and Raman spectroscopy confirm a rare terrestrial occurrence of monoclinic tridymite in clast-rich impact melt rock from the Eyreville B drill core in the Chesapeake Bay impact structure. The monoclinic tridymite occurs with quartz paramorphs after tridymite and K-feldspar in a microcrystalline groundmass of devitrified glass and Fe-rich smectite. Electron-microprobe analyses revealed that the tridymite and quartz paramorphs after tridymite contain different amounts of chemical impurities. Inspection by SEM showed that the tridymite crystal surfaces are smooth, whereas the quartz paramorphs contain irregular tabular voids. These voids may represent microporosity formed by volume decrease in the presence of fluid during transformation from tridymite to quartz, or skeletal growth in the original tridymite. Cristobalite locally rims spherulites within the same drill core interval. The occurrences of tridymite and cristobalite appear to be restricted to the thickest clast-rich impact melt body in the core at 1402.02–1407.49 m depth. Their formation and preservation in an alkali-rich, high-silica melt rock suggest initially high temperatures followed by rapid cooling.

American Mineralogist↗
USGS2011

Improved electron probe microanalysis of trace elements in quartz

Quartz occurs in a wide range of geologic environments throughout the Earth's crust. The concentration and distribution of trace elements in quartz provide information such as temperature and other physical conditions of formation. Trace element analyses with modern electron-probe microanalysis (EPMA) instruments can achieve 99% confidence detection of ~100 ppm with fairly minimal effort for many elements in samples of low to moderate average atomic number such as many common oxides and silicates. However, trace element measurements below 100 ppm in many materials are limited, not only by the precision of the background measurement, but also by the accuracy with which background levels are determined. A new "blank" correction algorithm has been developed and tested on both Cameca and JEOL instruments, which applies a quantitative correction to the emitted X-ray intensities during the iteration of the sample matrix correction based on a zero level (or known trace) abundance calibration standard. This iterated blank correction, when combined with improved background fit models, and an "aggregate" intensity calculation utilizing multiple spectrometer intensities in software for greater geometric efficiency, yields a detection limit of 2 to 3 ppm for Ti and 6 to 7 ppm for Al in quartz at 99% t-test confidence with similar levels for absolute accuracy.

American Mineralogist↗
USGS2011

Anatomy of a metabentonite: Nucleation and growth of illite crystals and their coalescence into mixed-layer illite/smectite

The illite layer content of mixed-layer illite/smectite (I/S) in a 2.5 m thick, zoned, metabentonite bed from Montana decreases regularly from the edges to the center of the bed. Traditional X-ray diffraction (XRD) pattern modeling using Markovian statistics indicated that this zonation results from a mixing in different proportions of smectite-rich R0 I/S and illite-rich R1 I/S, with each phase having a relatively constant illite layer content. However, a new method for modeling XRD patterns of I/S indicates that R0 and R1 I/S in these samples are not separate phases (in the mineralogical sense of the word), but that the samples are composed of illite crystals that have continuous distributions of crystal thicknesses, and of 1 nm thick smectite crystals. The shapes of these distributions indicate that the crystals were formed by simultaneous nucleation and growth. XRD patterns for R0 and R1 I/S arise by interparticle diffraction from a random stacking of the crystals, with swelling interlayers formed at interfaces between crystals from water or glycol that is sorbed on crystal surfaces. It is the thickness distributions of smectite and illite crystals (also termed fundamental particles, or Nadeau particles), rather than XRD patterns for mixed-layer I/S, that are the more reliable indicators of geologic history, because such distributions are composed of well-defined crystals that are not affected by differences in surface sorption and particle arrangements, and because their thickness distribution shapes conform to the predictions of crystal growth theory, which describes their genesis.

Montana↗
USGS2011

Visualizing trace element distribution in quartz using cathodoluminescence, electron microprobe, and laser ablation-inductively coupled plasma-mass spectrometry

Cathodoluminescent (CL) textures in quartz reveal successive histories of the physical and chemical fluctuations that accompany crystal growth. Such CL textures reflect trace element concentration variations that can be mapped by electron microprobe or laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Trace element maps in hydrothermal quartz from four different ore deposit types (Carlin-type Au, epithermal Ag, porphyry-Cu, and MVT Pb-Zn) reveal correlations among trace elements and between trace element concentrations and CL textures. The distributions of trace elements reflect variations in the physical and chemical conditions of quartz precipitation. These maps show that Al is the most abundant trace element in hydrothermal quartz. In crystals grown at temperatures below 300 °C, Al concentrations may vary by up to two orders of magnitude between adjacent growth zones, with no evidence for diffusion. The monovalent cations Li, Na, and K, where detectable, always correlate with Al, with Li being the most abundant of the three. In most samples, Al is more abundant than the combined total of the monovalent cations; however, in the MVT sample, molar Al/Li ratios are ~0.8. Antimony is present in concentrations up to ~120 ppm in epithermal quartz (~200–300 °C), but is not detectable in MVT, Carlin, or porphyry-Cu quartz. Concentrations of Sb do not correlate consistently with those of other trace elements or with CL textures. Titanium is only abundant enough to be mapped in quartz from porphyry-type ore deposits that precipitate at temperatures above ~400 °C. In such quartz, Ti concentration correlates positively with CL intensity, suggesting a causative relationship. In contrast, in quartz from other deposit types, there is no consistent correlation between concentrations of any trace element and CL intensity fluctuations.

American Mineralogist↗
USGS2013

Analysis of H 2 O in silicate glass using attenuated total reflectance (ATR) micro-FTIR spectroscopy

We present a calibration for attenuated total reflectance (ATR) micro-FTIR for analysis of H2O in hydrous glass. A Ge ATR accessory was used to measure evanescent wave absorption by H 2 O within hydrous rhyolite and other standards. Absorbance at 3450 cm −1 (representing total H 2 O or H 2 O t ) and 1630 cm −1 (molecular H 2 O or H 2 O m ) showed high correlation with measured H 2 O in the glasses as determined by transmission FTIR spectroscopy and manometry. For rhyolite, wt%H 2 O=245(±9)×A 3450 -0.22(±0.03) and wt%H 2 O m =235(±11)×A 1630 -0.20(±0.03) where A 3450 and A 1630 represent the ATR absorption at the relevant infrared wavelengths. The calibration permits determination of volatiles in singly polished glass samples with spot size down to ~5 μm (for H 2 O-rich samples) and detection limits of ~0.1 wt% H 2 O. Basaltic, basaltic andesite and dacitic glasses of known H 2 O concentrations fall along a density-adjusted calibration, indicating that ATR is relatively insensitive to glass composition, at least for calc-alkaline glasses. The following equation allows quantification of H 2 O in silicate glasses that range in composition from basalt to rhyolite: wt%H 2 O=(ω×A 3450 /ρ)+ b where ω = 550 ± 21, b = −0.19 ± 0.03, ρ = density, in g/cm 3 , and A 3450 is the ATR absorbance at 3450 cm −1 . The ATR micro-FTIR technique is less sensitive than transmission FTIR, but requires only a singly polished sample for quantitative results, thus minimizing time for sample preparation. Compared with specular reflectance, it is more sensitive and better suited for imaging of H 2 O variations in heterogeneous samples such as melt inclusions. One drawback is that the technique can damage fragile samples and we therefore recommend mounting of unknowns in epoxy prior to polishing. Our calibration should hold for any Ge ATR crystals with the same incident angle (31°). Use of a different crystal type or geometry would require measurement of several H 2 O-bearing standards to provide a crystal-specific calibration.

American Mineralogist↗
USGS2013

K-Ar dating and delta O-18-delta D characterization of nanometric illite from Ordovician K-bentonites of the Appalachians: illitization and the Acadian-Alleghenian tectonic activity

Nanometric (<0.02, 0.02–0.05, 0.05–0.1, 0.1–0.2 μm) illite fractions were separated from K-bentonite samples from northwestern Georgia, and studied by X-ray diffraction, oxygen and hydrogen isotope geochemistry, and K-Ar dated to more tightly constrain the tectono-thermal history of the Appalachian orogeny. Their XRD patterns are very similar for a given sample with respect to the peak shapes and positions. They are ordered illite-smectite mixed layers with only small variations in the relative proportions of illite and smectite interlayers. The illite crystal thickness distributions also are very homogeneous across the various size fractions of the same sample, but crystallite thickness varies from sample to sample. It can be concluded from the α-β 2 diagram that illitization occurred in all fractions by simultaneous nucleation and crystal growth, except for one sample. In that sample, a period of growth without nucleation was detected on top of the nucleation and growth episode. The K-Ar ages organize into two isochrons, the first at 319.9 ± 2.0 Ma with an initial 40 Ar/ 36 Ar ratio of 271 ± 66 Ma, and the second at 284.9 ± 1.2 Ma with an initial 40 Ar/ 36 Ar ratio of 310 ± 44. One data point above the older isochron and three between the two isochrons suggest a detrital contamination for the former separate and a possible further generation of nanoparticles for the three others. The samples with the older crystallization age consist of illite and illite-rich mixed-layers, and those with the younger age contain smectite-rich mixed-layers without illite, or illite-enriched illite-smectite mixed-layers. The K-Ar ages fit the age trends published previously for similar K-bentonites with regional age patterns between 240 and 270 Ma in the southwestern region, between 270 and 300 Ma in the central zone and the southern Appalachians, and between 315 and 370 Ma in the northernmost. Each of the two generations of illite crystals yields very consistent δ 18 O (V-SMOW) values at 17 ± 1‰ for the older and at 21 ± 1‰ for the younger. If crystallization temperatures of the nanometric illite were between 100 and 200 °C, as suggested by microthermometric determinations, the hydrothermal fluids had δ 18 O values of 4 ± 1‰ in the Dalton district and of 8 ± 1‰ in the Lafayette, Trenton, and Dirtseller districts at 100 °C, and of 11 ± 1 and 15 ± 1‰ in the same locations at 200 °C, probably because the water-rock isotope exchanges at elevated temperature occurred in rock-dominated systems. The δ 18 O of the fluids remained unchanged during local crystal growth, but varied depending on the geographic location of the samples and timing of illitization. The δD (V-SMOW) values of the different size fractions do not provide consistent information; they range from −70 to −45‰ for most nanometric and micrometric fractions (V-SMOW), but with no apparent coherent pattern. Nanometric illite-rich crystals from K-bentonite that underwent tectono-thermal alteration yield constant ages, constant clay mineralogy, constant crystallite size distributions for all of the nucleating and growing illite-type crystals of each sample, as well as constant δ 18 O values implying constant fluid chemistry, all pointing to geologically sudden crystallization.

Georgia↗
USGS1983

Orickite and coyoteite, two new sulfide minerals from Coyote Peak, Humboldt County, California.

Minute quantities of orickite and coyoteite occur with rare alkali iron sulphides in a mafic alkalic diatreme near Orick, Humboldt County. Orickite, NaxKyCu0.95Fe1.06zH2O (x,y < 0.03, z < 0.5), is hexagonal, a 3.695, c 6.16 A, D 4.212 g/cm3, Z = 4. The strongest XRD reflections are 3.08(100), 3.20(90), 2.84(60), 1.73(55), 1.583(30) A. The mineral is brass yellow, opaque, weakly pleochroic, but strongly anisotropic (greyish brown to greyish blue) in reflected light. Orickite is compositionally near to Fe-rich chalcopyrite, but it may be related to synthetic chalcogenides with a distorted wurtzite-(2H) structure. Coyoteite, NaFe3S5.2H2O, is triclinic, P1 or P1, a 7.409(8), b 9.881(6), c 6.441(3) A, alpha 100o25(3)', beta 104o37(5)', gamma 81o29(5)', D 2.879 g/cm3, Z = 2; strongest XRD reflections are 5.12(100), 7.13(90), 3.028(80), 3.080(70), 9.6(60), 5.60(60) A. Coyoteite is black, opaque, weakly pleochroic (pale brownish grey) and strongly anisotropic (grey to dull golden orange) in reflected light. It is unstable under normal atmospheric conditions. -J.A.Z.

American Mineralogist↗
USGS1983

Calorimetric investigation of the excess entropy of mixing in analbite-sanidine solid solutions: lack of evidence for Na,K short- range order and implications for two-feldspar thermometry.

Heat capacities (5-380 K) have been measured by adiabatic calorimetry for five highly disordered alkali feldspars (Ab99Or1, Ab85Or15, Ab55Or45, Ab25Or75 and Ab1Or99). The thermodynamic and mineralogical implications of the results are discussed. The new data are also combined with recent data for plagioclases in order to derive a revised expression for the two-feldspar thermometer. T calculated from the revised expression tend to be higher than previous calculations.-J.A.Z.

American Mineralogist↗
USGS1983

Hashemite, Ba(Cr,S)O4, a new mineral from Jordan.

Hashemite, Ba(Cr,S)O4, the isostructural chromate analogue of baryte, has been found in west-central Jordan. It is associated with chromian ettringite, apatite and calcite in a phosphatic carbonate rock analogous to the Hatrurim formation in Israel. The mineral is orthorhombic, Pnma, with a 9.112(2), b 5.541(1), c 7.343(1) A, Z = 4. Strongest XRD lines are 3.516(100), 3.171(80), 3.669(60), 2.175(60), 2.150(45) A. Hashemite occurs as small, euhedral, dark brown, commonly zoned crystals with an average D 4.59 g/cm3 and H. 31/2. It is biaxial positive; dark varieties have alpha 1.952(2), beta 1.960(2), gamma 1.977(2); light varieties have alpha 1.810(2), beta 1.813(2), gamma 1.824(2), 2Vgamma 35o-57o.-J.A.Z.

American Mineralogist↗
USGS1983

Heat capacty, relative enthalpy, and calorimetric entropy of silicate minerals: an empirical method of prediction.

Through the evaluation of experimental calorimetric data and estimates of the molar isobaric heat capacities, relative enthalpies and entropies of constituent oxides, a procedure for predicting the thermodynamic properties of silicates is developed. Estimates of the accuracy and precision of the technique and examples of its application are also presented. -J.A.Z.

American Mineralogist↗
USGS1982

Techniques for using iron crucibles in experimental igneous petrology.

Some iron crucibles contain impurities of Mn, Ti and other elements. Such impurities may alter the fO2 of the system and induce crucible-charge interactions. Pretreatment of impure iron crucibles in a CO2-CO atmosphere at 1050oC, under conditions slightly more reducing than Fe-Fe1-xO, minimizes undesirable changes in the bulk composition of the charge. -J.A.Z.

American Mineralogist↗