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News Article | March 1, 2017

The human handprint on the natural world has become evident in all too many ways in recent decades. The changing climate, the decline of wildlife and the loss of forests and other natural landscapes — all of these factors have led many scientists to conclude that we’re living in a new age they’ve dubbed the “Anthropocene,” in which the planet is dominated by human, rather than natural, influences. Now scientists have presented some stunning new evidence in support of this idea. They’ve found  human activity is responsible for a huge explosion in the diversity of minerals on Earth — possibly the biggest such event in the history of the planet, according to Robert Hazen, a scientist at the Carnegie Institution of Washington’s Geophysical Laboratory who led the new research. The last major mineral diversification event is believed to have occurred about 2 billion years ago. The research team, which includes Hazen and colleagues Marcus Origlieri and Robert Downs of the University of Arizona and Edward Grew of the University of Maine, published their findings Wednesday in the journal American Mineralogist. “Humans are doing this amazing increase in the number of crystals and the kinds of crystals that occur at or near a surface — and many of these minerals are going to persist for billions of years,” Hazen said. “If you’re a geologist who came back 100,000 years or a million or a billion years from now … you would find amazing mineralogical evidence of a completely different time.” The International Mineralogical Association (IMA) recognizes about 5,000 different mineral species. Every mineral must have a certain type of crystal structure, and it must be naturally occurring, forming on its own through geological processes. But the strict definition of a mineral may be growing a little hazier, Hazen said. For one thing, many of the minerals accepted by the IMA originate as a result of human activities, even if they technically form on their own. For example, there are many minerals associated with mining. They form on the walls of mine tunnels or precipitate out of mine water. Others have been found in piping systems or on metal artifacts, and at least one new mineral was discovered in a storage cabinet in a museum, Hazen said. After an exhaustive look through the 5,000 IMA-official minerals, the researchers concluded that 208 of them are the inadvertent result of human activities. Additionally, humans have produced a huge assortment of mineral-like crystals through deliberate chemical processes. But they’re not defined as true minerals because they didn’t arise “naturally.” For instance, there are mineral-like compounds produced specifically for use in cement, magnets, batteries, synthetic gemstones and a wide variety of other commercial applications. Altogether, there are tens of thousands of these mineral-like compounds. The Inorganic Crystal Structure Database lists 180,000, the researchers note in the paper, adding: “the Anthropocene Epoch is an era of unparalleled inorganic compound diversification.” There’s been some debate among scientists across all fields about when the Anthropocene era began. Climate scientists have pointed to the industrial revolution, which marked the beginning of large-scale greenhouse gas emissions and the rapid, human-caused warming of the atmosphere. From a mineralogical perspective, scientists are finding human-mediated minerals on structures or artifacts dating back thousands of years. But Hazen added that the biggest diversity explosion “comes with the rise of chemistry about the time of 1800, very close to the industrial revolution — and that’s where you see this incredible spike, the greatest diversification of crystals on earth.” The huge human-mediated diversity of minerals is a major way mankind will leave its mark on geological history, but there are other signs humans will probably leave behind as well. For instance, humans are not only responsible for the creation of all kinds of minerals and mineral compounds but they’ve also been carting them all over the planet. The jewelry business, for instance, has led to the trade of mineral gems all over the world. Thousands of years from now, there will be rubies and sapphires lying around in places they would have never naturally formed. Human engineering and construction is also likely to leave a permanent mark on the geological landscape. “The largest impacts are our roads, our buildings, our cities — places where we have huge quantities of transported stones and stone-like materials,” Hazen said. These materials will persist, even as they become covered with layers upon layers of sediments over thousands of years, leading to large buried deposits of stone and mineral that only exist in that location because humans placed them there long ago. Perhaps more than anything, the paper’s findings speak to the power and long-lasting influence of human innovation. This effect has manifested in a variety of environmentally destructive ways over the past century from climate change, air and water pollution to sharp declines in plants and animals. But from a mineralogical perspective, there’s also evidence of the “boundless” nature of human creativity, Hazen said. “We’re talking about a time of declining biodiversity, but thanks to human ingenuity, we have a time of increased crystal diversity,” he said. “In fact, the greatest increase in the history of the globe.”

Mysen B.O.,Geophysical Laboratory | Tomita T.,Tohoku University | Ohtani E.,Tohoku University | Suzuki A.A.,Tohoku University
American Mineralogist | Year: 2014

Speciation of D-O-H-C-N volatiles in alkali aluminosilicate melts and of silicate in D-O-H-C-N fluid has been determined in situ to 800 °C and >2 GPa under reducing and oxidizing conditions by using an externally heated hydrothermal diamond-anvil cell with Raman spectroscopy as the structural probe. Reducing conditions were near those of the IW oxygen buffer, whereas oxidizing conditions were obtained by conducting the experiments with oxidized components only and with Pt as a catalyst. Raman bands assigned to C-H stretching in CHxDy isotopologues and CH4 groups (including CH3) were employed to determine the CH4/CH xDy ratio in fluids and melts. This ratio decreases from 1.5-2 at 500 °C to between 1.2 and 1 with 800 °C with ΔH-values of 13.6 ± 2.1 and 5.5 ± 1.1 kJ/mol for melt and fluid, respectively. The CH4/CHxDy fluid/melt partition coefficient ranges between ∼16 and ∼3 with ΔH = 33 ± 6 kJ/mol assuming no pressure effect. This behavior of deuterated and protonated complexes is ascribed to speciation of volatile and silicate components in fluids and melts in a manner that is conceptually similar to D/H partitioning among complexes and phases in brines and hydrous silicate systems. Molecular N2 is the N-bearing species in fluids and melts under oxidizing conditions. Under reducing conditions, the dominant species are molecular NH3 and ammine groups, NH2-. The NH3/NH2 ratio varies between 0.15 and 0.75 in the 425-800 °C temperature range. The enthalpy change of the ammonia/ammine equilibrium, ΔH, derived from the temperature and assuming no pressure effect on the equilibrium, is 19 ± 8 and 61 ± 9 kJ/mol for melt and fluid, respectively. The fluid/melt partition coefficient, (NH3 + NH2-)fluid/ (NH3 + NH2-)melt, ranges from 8 to 3 with ΔH = 45 ± 12 kJ/mol. For oxidized nitrogen, the fluid/melt partition coefficient is twice or more of those values for reduced nitrogen. Hydrogen bonding can be detected at 500 °C and below. This behavior resembles that of H2O. Deuterium-containing analogues of the (N+H)-species could not be detected with precision because these were in the frequency-range of the second-order Raman shift of diamond in the diamond-anvil cell itself and could not be isolated from the strong background generated by the Raman intensity from the diamond. These results imply that, unlike noble gases, degassing of N-bearing species from the mantle is redox dependent, and is also more efficient at lower temperatures (shallow depths). Reduced and oxidized C-O-H-N species exist fluids and melts in the modern mantle, whereas reduced species dominated in the young Earth. The fH2-dependent speciation C-O-H-N volatile components result in fH2-dependent thermodynamic and transport properties of fluids and melts in the interior of the Earth and terrestrial planets. In fluids, the solubility of nominally incompatible trace elements can increase by orders of magnitude upon its saturation with silicate components. Trace element and stable isotope partitioning between fluids and melt can change by >100% for the same reason.

Roskosz M.,Lille University of Science and Technology | Bouhifd M.A.,University of Oxford | Bouhifd M.A.,CNRS Magmas and Volcanoes Laboratory | Jephcoat A.P.,University of Oxford | And 2 more authors.
Geochimica et Cosmochimica Acta | Year: 2013

Nitrogen is the dominant gas in Earth atmosphere, but its behavior during the Earth' differentiation is poorly known. To aid in identifying the main reservoirs of nitrogen in the Earth, nitrogen solubility was determined experimentally in a mixture of molten CI-chondrite model composition and (Fe, Ni) metal alloy liquid. Experiments were performed in a laser-heated diamond-anvil cell at pressures to 18GPa and temperatures to 2850±200K. Multi-anvil experiments were also performed at 5 and 10GPa and 2390±50K. The nitrogen content increases with pressure in both metal and silicate reservoirs. It also increases with the iron content of the (Fe, Ni) alloy. Sieverts' formalism successfully describes the nitrogen solubility in metals up to 18GPa. Henry's law applies to nitrogen-saturated silicate melts up to 4-5GPa. Independently of these solubility models, it is shown that the partition coefficient of nitrogen between metal and silicate melts changes from almost 104 at ambient pressure to about 10-20 for pressures higher than 1GPa. The pressure-dependence of the nitrogen partitioning can explain the recently suggested depletion of nitrogen relative to other volatiles in the bulk silicate Earth. © 2013 Elsevier Ltd.

News Article | February 14, 2016

Throughout the known universe, the Earth is considered significantly distinct from other planets and cosmic objects because it is the only home to living beings. In fact, our planet's ability to host life may be linked to the existence of rare minerals, differentiating it from others in the cosmos. In a new study that catalogued minerals on Earth, a pair of scientists found that there are about 2,550 rare minerals that make up our planet's unique fingerprint. Research scientists Robert Hazen and Jesse Ausubel teamed up to classify the most singular minerals on the planet, such as the Sardinian ichnusaite as well as the amosite and the fingerita found in El Salvador. The pair found that there is an association between the presence of minerals on Earth and the planet's ability to sustain life. "Life depends on minerals," says Hazen, a scientist at the Geophysical Laboratory in the Carnegie Institution of Washington. "Life could not have begun without some of the chemical properties that minerals provided at Earth's beginning." Their conclusion is that each planet with the ability to support life has a unique fingerprint of rare minerals. It's also very likely that planets such as Mercury and Mars have much simpler minerals because they cannot sustain life. Hazen, who is also the executive director of the Deep Carbon Observatory that examines carbon on Earth, says that explorations performed by rovers on the moon and on Mars are not finding anything very surprising in the field of mineralogy because of this reason. Ausubel, a senior research associate in New York City's Rockefeller University, says the mineral resources on Earth are linked to the planet's richness of life. A planet that is ecologically poorer is equal to a planet with a presence of fewer minerals. Additionally, none of the 2,550 minerals identified in the study is located in more than five locations, which means they are "the rarest of the rare." For some of the minerals, the supply is so scarce that it could fit in a thimble. But hunting down these odd minerals are important because they are fundamentally vital to understanding the construction of our planet. Hazen and Ausubel divided the 2,550 minerals into four broad categories of rarity, depending on the conditions in which they form, how rare their ingredients are, how ephemeral they are and the limitations of their supply. Incidentally, there is one entry in the catalogue that is named after Hazen. "Hazenite" is only found in Mono Lake in California and forms when the phosphorus concentration in the lake reaches high levels. The microbes in the water have to start excreting hazenite from their cells in order to survive. The tiny, colorless crystals are essentially microbial "poop." "Yes, it's true - hazenite happens," adds Hazen. Hazen and Ausubel's findings are featured in the magazine American Mineralogist.

The structure of H2O-saturated silicate melts and of silicate-saturated aqueous solutions, as well as that of supercritical silicate-rich aqueous liquids, has been characterized in-situ while the sample was at high temperature (to 800°C) and pressure (up to 796MPa). Structural information was obtained with confocal microRaman and with FTIR spectroscopy. Two Al-bearing glasses compositionally along the join Na2O•4SiO2-Na2O•4(NaAl)O2-H2O (5 and 10mol% Al2O3, denoted NA5 and NA10) were used as starting materials. Fluids and melts were examined along pressure-temperature trajectories of isochores of H2O at nominal densities (from PVT properties of pure H2O) of 0.85g/cm3 (NA10 experiments) and 0.86g/cm3 (NA5 experiments) with the aluminosilicate+H2O sample contained in an externally-heated, Ir-gasketed hydrothermal diamond anvil cell.Molecular H2O (H2O°) and OH groups that form bonds with cations exist in all three phases. The OH/H2O° ratio is positively correlated with temperature and pressure (and, therefore, fugacity of H2O, fH2O) with (OH/H2O°)melt>(OH/H2O°)fluid at all pressures and temperatures. Structural units of Q3, Q2, Q1, and Q0 type occur together in fluids, in melts, and, when outside the two-phase melt+fluid boundary, in single-phase liquids. The abundance of Q0 and Q1 increases and Q2 and Q3 decrease with fH2O. Therefore, the NBO/T (nonbridging oxygen per tetrahedrally coordination cations), of melt is a positive function of fH2O. The NBO/T of silicate in coexisting aqueous fluid, although greater than in melt, is less sensitive to fH2O.The melt structural data are used to describe relationships between activity of H2O and melting phase relations of silicate systems at high pressure and temperature. The data were also combined with available partial molar configurational heat capacity of Qn-species in melts to illustrate how these quantities can be employed to estimate relationships between heat capacity of melts and their H2O content. © 2010 Elsevier Ltd.

Mysen B.O.,Geophysical Laboratory | Yamashita S.,Okayama University
Geochimica et Cosmochimica Acta | Year: 2010

The structure of silicate melts in the system Na2O·4SiO2 saturated with reduced C-O-H volatile components and of coexisting silicate-saturated C-O-H solutions has been determined in a hydrothermal diamond anvil cell (HDAC) by using confocal microRaman and FTIR spectroscopy as structural probes. The experiments were conducted in-situ with the melt and fluid at high temperature (up to 800°C) and pressure (up to 1435MPa). Redox conditions in the HDAC were controlled with the reaction, Mo+H2O=MoO2+H2, which is slightly more reducing than the Fe+H2O=FeO+H2 buffer at 800°C and less.The dominant species in the fluid are CH4+H2O together with minor amounts of molecular H2 and an undersaturated hydrocarbon species. In coexisting melt, CH3 - groups linked to the silicate melt structure via Si-O-CH3 bonding may dominate and possibly coexists with molecular CH4. The abundance ratio of CH3 - groups in melts relative to CH4 in fluids increases from 0.01 to 0.07 between 500 and 800°C. Carbon-bearing species in melts were not detected at temperatures and pressures below 400°C and 730MPa, respectively. A schematic solution mechanism is, Si-O-Si+CH4Si-O-CH3+H-O-Si. This mechanism causes depolymerization of silicate melts. Solution of reduced (C-O-H) components will, therefore, affect melt properties in a manner resembling dissolved H2O. © 2010 Elsevier Ltd.

The behavior of melts and fluids is at the core of understanding formation and evolution of the Earth. To advance our understanding of their role, high-pressure/-temperature experiments were employed to determine melt and fluid structure together with carbon isotope partitioning within and between (CH4+H2O+H2)-saturated aluminosilicate melts and (CH4+H2O+H2)-fluids. The samples were characterized with vibrational spectroscopy while at temperatures and pressures from 475° to 850 °C and 92 to 1158 MPa, respectively.The solution equilibrium is 2CH4+Qn=2CH3 -+H2O+Qn+1 where the superscript, n, in the Qn-notation describes silicate species where n denotes the number of bridging oxygen. The solution equilibrium affects the carbon isotope fractionation factor between melt and fluid, αmelt/fluid. Moreover, it is significantly temperature-dependent. The αmelt/fluid<1 with temperatures less than about 1050 °C, and is greater than 1 at higher temperature.Methane-bearing melts can exist in the upper mantle at fO2≤fO2(MW) (Mysen et al., 2011). Reduced (CH)-species in present-day upper mantle magma, therefore, are likely. During melting and crystallization in this environment, the δ13C of melts increases with temperature at a rate of ~0.6‰/°C. From the simple-system data presented here, at T≤1050°C, melt in equilibrium with a peridotite-(CH4+H2O+H2)-bearing mantle source will be isotopically lighter than fluid. At higher temperatures, melts will be isotopically heavier. Degassing at T≤1050°C will shift δ13C of degassed magma to more positive values, whereas degassing at T≥1050°C, will reduce the δ13C of the degassed magma. © 2016 Elsevier B.V.

The C-O-H-N solubility and solution mechanisms in silicate melts and C-O-H-N speciation in coexisting fluid to upper mantle temperatures and pressures and with redox conditions from the MH to the IW buffer are discussed. Focus is on in-situ structural characterization of coexisting melt and fluid. In fluid+melt-COH, fluid+melt-NOH, and fluid+melt-OH systems, volatiles are dissolved in molecular form (CO2, CH4, NH3, N2, H2O, H2) and as complexes that form chemical bonding with the silicate network (CO3, CH3, NH2, OH).In silicate-OH systems molecular H2O (H2OÚ) and OH-groups exist in silicate- and aluminosilicate-saturated fluids and coexisting water-saturated melts above ~400°C and ~0.5GPa with their OH/H2OÚ-ratio positively correlated with temperature. The extent of hydrogen bonding in both fluids and melts diminishes with temperature so that above ~400°C it cannot be detected. The incrementH of hydrogen bonding in aqueous fluid (22±1kJ/mol) is about twice that in silicate melts (10±2kJ/mol). Silicate speciation in silicate-saturated fluid and hydrous silicate melts comprises similar Q-species with incrementH of the solution reactions in silicate-saturated fluid, water-saturated melt, and supercritical fluid ~400kJ/mol.In COH-silicate systems methane solubility in melt increases from 0.2wt.% to ~0.5wt.% in the melt NBO/Si range from 0.4 to 1.0 at 1-2.5GPa and 1400°C. The solubility increases by ~150% between the redox conditions of the IW and MH buffers. At the NNO buffer conditions and more oxidizing, carbon exists as carbonate complexes in melts and as CO2 in fluid. Reduced (C+H)-bearing species in melts (CH3-groups and molecular CH4) are stable at fH2(MW) and more reducing conditions, whereas the species in coexisting fluid are CH4, H2, and H2O.In NOH-silicate systems, the N solubility in melt decreases from 0.98 to 0.28wt.% in the melt NBO/Si-range from 0.4 to 1.18 at the redox conditions of the IW buffer. The solubility decreases by about 50% between the redox conditions of the IW and MH buffers. At IW, nitrogen occurs in silicate melts amine groups, NH2, bonded to the silicate network, and as molecular NH3, whereas in coexisting NOH fluids the dominant species are NH3, N2, H2 and H2O. The NH2 -/NH3 abundance ratio varies by ~55 between melt compositions with NBO/Si=1.18 and 0.4. In fluids and melts, decreasing hydrogen fugacity leads to oxidation of nitrogen to form molecular N2 so that at the MH redox conditions, the dominant N-bearing species is N2.The redox-dependent solution mechanisms of COHN volatile components in silicate melts affect their structure differently, which results in redox-dependent thermodynamic and transport properties of magmatic liquids in the interior of the Earth and terrestrial planets. These properties include mineral/melt minor and trace element partitioning, melt/fluid isotope fractionation, and transport and thermodynamic properties of melt saturated with variably-oxidized COHN volatile components. © 2012 Elsevier B.V.

Howie R.T.,University of Edinburgh | Guillaume C.L.,University of Edinburgh | Scheler T.,University of Edinburgh | Goncharov A.F.,Geophysical Laboratory | Gregoryanz E.,University of Edinburgh
Physical Review Letters | Year: 2012

We used Raman and visible transmission spectroscopy to investigate dense hydrogen (deuterium) up to 315 (275) GPa at 300 K. At around 200 GPa, we observe the phase transformation, which we attribute to phase III, previously observed only at low temperatures. This is succeeded at 220 GPa by a reversible transformation to a new phase, IV, characterized by the simultaneous appearance of the second vibrational fundamental and new low-frequency phonon excitations and a dramatic softening and broadening of the first vibrational fundamental mode. The optical transmission spectra of phase IV show an overall increase of absorption and a closing band gap which reaches 1.8 eV at 315 GPa. Analysis of the Raman spectra suggests that phase IV is a mixture of graphenelike layers, consisting of elongated H 2 dimers experiencing large pairing fluctuations, and unbound H 2 molecules. © 2012 American Physical Society.

Structural characterization of silicate melts and aqueous fluids equilibrated at pressures and temperatures corresponding to the Earth's interior requires measurements in-situ while the samples are at the pressure and temperature of interest. To this end, structure and structure-property relations of melts and coexisting fluids in silicate-COH systems have been determined at temperatures up to 1000 °C and at pressures to ~ 2.0 GPa. The water component of silicate-H 2O systems shows aqueous fluids, supercritical fluids, and hydrous melts to comprise molecular H 2O (H 2O 0) and OH-groups, bonded to Si 4+ and likely Al 3+. The abundance-ratio, OH/H 2O 0, is positively correlated with temperature. The extent of hydrogen bonding diminishes with temperature and cannot be detected at above ~450°C and ~0.4GPa. Its {increment}H is near 10kJ/mol for water dissolved in hydrous melt as compared with ≥20kJ/mol for pure H 2O. Hydrogen bonding cannot, therefore, be the cause of property behavior in hydrous magmatic systems because the temperature in hydrous magmatic systems exceeds 600°C. In SiO 2-H 2O fluid, silicate solute comprises Q 0 and Q 1 species with a {increment}H of the polymerization reaction of ~15kJ/mol assuming no pressure effect. In the Q n-notations, the value of n indicates the number of bridging oxygen in a silicate or aluminosilicate polymeric species. In chemically more complex alkali aluminosilicate systems, the silicate speciation in melts, in aqueous fluid, and in supercritical fluids comprises the same Q-species, but their abundance and proportions differ with the more polymerized species dominant in melt. Silicate-water interaction in the fluids, melts and supercritical fluids is described with the expression, 12Q 3+13H 2O⇋2Q 2+6Q 1+4Q 0 with {increment}H=400-450kJ/mol. The solubility of geochemically important trace elements such as, for example, HFSE in silicate-saturated aqueous fluid under deep crustal and upper mantle pressure and temperature conditions is orders of magnitude greater than in pure H 2O at the same temperature and pressure. For example, the fluid/melt partition coefficients for structural species such as PO 4, P 2O 7 and Q nP are in the 0.15-0.7 range and increases rapidly with silica content of the fluid. The fluid/melt partition coefficient of TiO n species in similar Ti-bearing systems increases from ~0.1 to ~0.5 in the 200°-500°C and ~0.4-1.0GPa temperature and pressure range. The Ti abundance in aqueous fluids coexisting with rutile in the same pressure and temperature range is about 2 orders of magnitude lower. These differences reflect solute-dependent structural roles of Ti 4+ and P 5+ in pure H 2O fluid and in silicate-saturated H 2O. Other HFSE likely behave similarly. In silicate melt-COH systems, oxygen fugacity (f O2) is an additional variable affecting solubility and solution mechanisms. From haplobasalt to haploandesite melt-COH, the carbon solubility at upper mantle pressures and temperatures decreases from ~2wt.% to ~1wt.% in equilibrium with CO 2 gas. Oxidized carbon is dissolved dominantly as CO 3 groups. The solubility of reduced carbon in the COH system, on the other hand, is less than 50% of oxidized carbon. Reduced carbon in the COH system is dissolved in melts as a mixture of CH 3 groups and CH 4 molecules when coexisting fluid is CH 4. The isotope fractionation between coexisting COH-saturated silicate melt and silicate-saturated COH fluid is correlated with the CH 3/CH 4 abundance ratio in the melt. By changing f O2 from oxidized to reduced, resultant changes of C solution mechanisms in melt-COH systems cause NBO/T changes. This change can cause crystal/melt element partition coefficients to vary by several tens of percent within natural abundance ranges of COH in magmatic liquids. Variable redox conditions will also result in variable Q-speciation of melts. This variability, in turn, governs configurational properties of magmatic liquids. As a result, their transport properties such as viscosity and diffusion also vary with redox conditions. © 2012 Elsevier B.V.

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