Non-crystalline Minerals Research Articles

Carbon sequestration within millet phytoliths from dry-farming of crops in China

Phytoliths are noncrystalline minerals that form inside cells and cell walls of different parts of plants. Organic carbon in living cells can be occluded in phytoliths during plant growth. It has been documented that the occluded carbon within phytoliths is an important long-term terrestrial carbon reservoir that has a major role in the global carbon cycle. Common millet and foxtail millet have become typical dry-farming crops in China since the Neolithic Age. The study of carbon conservation within phytoliths in these crops could provide insights into anthropogenic influences on the carbon cycle. In this study, we analyzed the carbon content in phytoliths of common millet and foxtail millet. The results indicated that (1) common millet and foxtail millet contained 0.136% ± 0.070% and 0.129%± 0.085% phytolith-occluded carbon (PhytOC) on a dry mass basis, respectively; (2) based on the mean annual production of common millet and foxtail millet in the last 10 years, the phytolith occluded carbon accumulation rate of common millet and foxtail millet was approximately 0.023 ± 0.015 and 0.020± 0.010 t CO2 ha−1 a−1, respectively; (3) assuming a similar phytolith occluded carbon accumulation rate as for common millet (the highest accumulation rate was 0.038 t CO2 ha−1 a−1), this could result in the sequestration of 2.37 × 106 t CO2 per year for the 62.4 × 106 ha dry-farming crops in China. Although there was a decline in the annual production rate and planting area of foxtail millet during 1949 to 2008, the total phytolith carbon sequestration rate was 7×106 t CO2 within the 60-year period. However, phytolith occluded carbon has not yet been fully considered as a global carbon sink. Also, this carbon fraction is probably one of the best candidates for the missing carbon sink.

Changes in the Chemical and Mineralogical Properties of Mt. Talang Volcanic Ash in West Sumatra during the Initial Weathering Phase

Eruptions from Talang volcano on 12 April 2005 distributed volcanic ash over portions of the Solok District of West Sumatra, Indonesia. Unleached and leached pristine volcanic ash were collected immediately after the eruption, and the third sample was collected after 2 years. The mineralogy and chemical properties of pristine volcanic ash and volcanic ash deposits that were weathered for 2 years from the 2005 eruption of Mt. Talang, Sumatra, were studied to characterize the volcanic ash, identify the primary minerals present, and determine its chemical properties. Results showed that the volcanic ash contained 30% noncrystalline minerals (or volcanic glass); the remaining ash is composed of crystalline minerals such as labradorite, hypersthene, augite, hornblende, olivine, opaque ferromagnetic minerals, and rock fragments. Notable differences in pH values were observed as the pH tended to become more acidic from the unleached, leached, and weathered volcanic ash, but the ash did not give much response to the sodium fluoride (NaF) test. Total sulfur gradually decreased from 3.28% in unleached ash to 1.93% after 2 years. Available phosphorus (P) in the unleached volcanic ash was 68 mg kg−1, and this value was decreased by 15 % after 2 years of being exposed to the atmosphere, while phosphate retention ranged between 52.8% and 66.8%. Cation exchange capacity (CEC) was low with the value of 10 cmolc kg−1 although base saturation was high, exceeding 75%. The low acid oxalate–extractable silicon (Si), aluminum (Al), and iron (Fe) values of 0.07%, 0.25% and 1.17%, respectively, show the scarcity of secondary amorphous compounds in the ash. Total elemental analysis indicated that no differences were found in total silica oxide (SiO2) content of all samples, with a value about 56%, and this volcanic ash can be classified as basaltic andesite. We observed that removal of chemical elements by leaching was large for calcium oxide (CaO), magnesium oxide (MgO), and sodium oxide (Na2O) as the values decreased in time. Solid-state 29Si and 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) studies indicated that Al occurred in both tetrahedral and octahedral forms. Silicon was not present in the tetrahedral layer. An intense peak at −92 ppm was indicative of the presence of aluminosilicates.

Soil formation overlying volcanic materials at Mount Erenler, Konya, Turkey

Studies of soils developed on volcanic materials are insufficient in Turkey in light of the wide distribution of these soils. The objectives of the present work were to assess the influence of climate and other soil-forming factors on physical, chemical, and mineralogical characteristics and pedological processes in the soil genesis and soil classification of 4 volcanic soil profiles derived from andesitic parent material, and to determine whether they meet the requirements for classification as Andisols. Collected from a semiarid climate in Konya, Turkey, these soils are characterized as medium- and fine-textured with low organic matter content, low cation exchange capacity, and low soil moisture retention. Bulk density was greater than 0.90 g cm^{-3} in all profiles. In general, phosphate retention was low, and lower than 85% in all profiles. The Al + ½ Fe percentages (by ammonium oxalate) were lower than 2% in all profiles. The pH values in NaF were less than 9.5 in the soils studied. Selective extraction yielded the following relationship in all extractions: Fe_d > Fe_o > Fe_p. Additionally, in most horizons: Al_p > Al_o > Al_d. According to selective dissolution analysis results and index values, noncrystalline minerals such as allophane, imogolite, and iron-humus complexes have not formed in these soils. Only noncrystalline minerals were present, such as Al-humus complexes in great quantities, and, in small quantities, ferrihydrite. Crystallized Fe minerals were more common than other Fe minerals. Feldspar, cristobalite, and quartz were the most common primer minerals. Hematite, cummingtonite, and magnetite were also found in some profiles. X-ray diffraction indicated that kaolinite and illite were dominant minerals in the clay fraction; furthermore, a considerable amount of smectite was found in the clay fraction. The local climate, characterized by low precipitation and a long dry season, obstructs the formation of andic soil properties because of the low rate of weathering and inadequate Si leaching. As a result, the soils of Mount Erenler were not classified as Andisol but rather as Entisol. The major factors determining soil genesis on Mount Erenler appear to be climate, topography, and the nature of the parent material

Stabilization of recent soil carbon in the humid tropics following land use changes: evidence from aggregate fractionation and stable isotope analyses

Quantitative knowledge of stabilization- and decomposition processes is necessary to understand, assess and predict effects of land use changes on storage and stability of soil organic carbon (soil C) in the tropics. Although it is well documented that different soil types have different soil C stocks, it is presently unknown how different soil types affect the stability of recently formed soil C. Here, we analyze the main controls of soil C storage in the top 0.1 m of soils developed on Tertiary sediments and soils developed on volcanic ashes. Using a combination of fractionation techniques with 13C isotopes analyses we had the opportunity to trace origin and stability of soil carbon in different aggregate fractions under pasture and secondary forest. Soil C contents were higher in volcanic ash soils (47–130 g kg−1) than in sedimentary soils (19–50 g kg−1). Mean residence time (MRT) of forest-derived carbon in pastures increased from 37 to 57 years with increasing silt + clay content in sedimentary soils, but was independent from soil properties in volcanic ash soils. MRTs of pasture-derived carbon in secondary forests were considerably shorter, especially in volcanic ash soils, where no pasture-derived carbon could be detected in any of the four studied secondary forests. The implications of these results are that the MRT of recently incorporated organic carbon depends on clay mineralogy and is longer in soils dominated by smectite than non-crystalline minerals. Our results show that the presence of soil C stabilization processes, does not necessarily mean that recent incorporated soil C will also be effectively stabilized.

Genesis of soils across a late Quaternary volcanic landscape in the humid tropical island of Leyte, Philippines

This study evaluated the characteristics and genesis of soils across a young volcanic landscape in the humid tropical island of Leyte, Philippines. Five representative soil pedons (P1–P5) derived from late Quaternary volcanoclastics (i.e. fragmental) on a hillslope sequence were examined and sampled. Results revealed that the soils have generally similar morphological characteristics particularly in terms of soil colour (10YR 3/3–10YR 5/6) and soil structure (granular to subangular blocky), but differed in terms of soil thickness and clay content, which was higher in P3 than the other pedons across the landscape. The high porosities of the soils were the results of high organic matter, the dominance of noncrystalline (short-range order) minerals, as well as the isovolumetric weathering in the subsoils. All soils have very similar chemical properties (e.g. acidic, high organic carbon, low exchangeable bases), except soils from the middle backslope position (P3), which have high cation exchange capacity because higher exchangeable Ca and K result in a higher base saturation. Allophane, goethite, ferrihydrite, and gibbsite are the dominant clay minerals in the soils. Principal component analysis revealed that P3 was distinct from pedons P1, P2, P4, and P5, suggesting that it was substantially different from all other soils across the landscape. Soil formation was relatively fast due to the easy weatherability of the parent materials, high rainfall, and good drainage of the soils along the landscape. This study revealed that on young volcanic soils under humid tropical condition, topography greatly influenced soil development.

Sorption-Desorption Processes of Metals and Metalloids in Soil Environments

Trace elements may be present in solution with positive or negative charges and in different redox state. They occur predominantly in cationic form (Pb, Cu, Zn, Ni, Cd, Hg, Cr(III), Co) but some trace elements are present in anionic form (As, Se, Cr(VI), Mo and B). In soil environments, sorption/desorption reactions on/from inorganic and organic sorbents control the concentration of metals and metalloids in solution and affect their bioavailability, leaching and toxicity. Sorption-desorption processes of elements in cationic form differ greatly from those in anionic form. These reactions are affected by many factors, such as pH, nature of the sorbents, presence and concentration of organic and inorganic ligands, including humic and fulvic acids, root exudates and nutrients. Furthermore, redox reactions, both biotic and abiotic, are of great importance in controlling the oxidation state and thus, the mobility, the phytoavailability and the toxicity of many elements, such as Cr, Se, Co, Pb, As, Ni and Cu (Kabata-Pendias, 2001; Huang and Germida, 2002; Violante et al., 2002; Sparks, 2003; Huang and Gobran, 2005; Violante et al., 2007). The aim of this presentation is to provide information on the factors which affect the mobility of trace elements. Special attention is devoted to the influence of inorganic and organic ligands, including nutrients and root exudates, on the sorption/desorption processes of trace elements in cationic and anionic forms on/from soil components, soils and selected synthetic minerals (double layered hydroxides, the so called “anionic clays”). The soil components responsible for trace element sorption include, soil humic substances, phyllosilicates, carbonates and variable charge minerals (constituents such as Fe, Al, Mn and Ti oxides, short-range ordered aluminosilicates as well as phyllosilicates coated by OH-Al or OH-Fe species whose charge varies with the pH of the soil solution). Recently, evidence on the sorption of heavy metals on microorganisms have been reported (Jackson, 1998). Soil components differ greatly in their sorption capacities, their cation and anion exchange capacities, and the binding energies of their sorption sites. Trace element sorption kinetics depend on the type of surface and trace element, but generally are rapid. Half times for bivalent cations, such as Pb, Zn, Cu and Cd, sorption on peat range from 5 to 15 seconds. Except for some noncrystalline minerals that have very high specific surface charge density with highly reactive sites, humic substances appear to have the greatest capacity for sorption of trace elements in cationic form. A body of evidence has demonstrated that humic matter and metal oxides are much more effective scavengers of trace elements in cationic form, than even the most efficient sorbent among phyllosilicates, indicating that specific sorption and other complexation processes are the dominant binding mechanisms (Jackson, 1998; Huang and Germida, 2002; Spark, 2003). Complexation reactions have the following effects: i) metal ions are prevented from being precipitated; ii) complexing agents can act as carriers for trace elements in soil solution; iii) their toxicity is often reduced by complexation.

Investigation of soils developed on volcanic materials in Nisyros Island, Greece

Soils that are forming on volcanic parent materials have unique physical and chemical properties and in most cases, on wet and humid climates, are classified as Andisols. The main purpose of this study is to examine if the soils that are forming on volcanic materials under a dry Mediterranean climate, in Nisyros Island (Greece), meet the requirements to be classified as Andisols. Soils from seven sites were sampled and examined for their main physico-chemical properties and selective dissolution analysis. Dithionite–citrate–bicarbonate (DCB) extractable Al and Fe (Ál d, Fe d), acid ammonium oxalate extractable Al, Fe, and Si (Ál o, Fe o and Si o), and sodium pyrophosphate extractable Al and Fe (Al p, Fe p) were measured. In addition, Al and Si were determined after reaction with hot 0.5 M NaOH, (Al NaOH and Si NaOH) and with Tiron-(C 6H 4Na 2O 8S 2), (Al T and Si T). P-retention was also measured. The soils are characterised by coarse texture, low organic matter content, low values of cation exchange capacity (CEC), and high pH values. Values of Si o, Al o and Fe o are less than 0.022%, 0.09% and 0.35% respectively, highlighting the lack of noncrystalline components. The ratio (Fe d–Fe o)100/Fe d is quite high expressing the degree of crystallisation of free iron oxides. For all samples tested, values of the Al o + 1/2Fe o index are extremely low (< 0.24%). High Si NaOH and Si T (arising 2.76% and 2.18% respectively) indicate the presence of silica in amorphous forms. P-retention values are very low (< 12.6%). The results indicated the absence of noncrystalline minerals except for amorphous silica, and do not exhibit andic or vitric soil characteristics to be classified as Andisols.

Soils developed on volcanic materials in the island of Thera, Greece

Samples were taken of soils formed on volcanic material, primarily composed of rhyodacitic pumice, on the island of Thera, Greece (South Aegean Sea, Southeastern Mediterranean), and analyses for physical and chemical properties carried out. These soils are characterised as having a coarse texture, low organic matter content, low cation exchange capacity (CEC) and soil moisture retention, but a high pH despite the acidic nature of the parent material. Extraction with sodium dithionite–citrate, acid ammonium oxalate, sodium pyrophosphate and hot 0.5 M NaOH showed that, in contrast to soils usually forming on volcanic material worldwide, soils lack noncrystalline minerals like allophane, imogolite, ferrihydrite and iron and aluminium humus complexes. The only noncrystalline mineral present and, in great quantities, is amorphous silica. Winds, prevailing practically all year round, transfer droplets of seawater to these soils which in combination with the great porosity, relatively high sodium content of the parent material and low rainfall are the primary factors in the poor development of these soils and high pH. No andic properties are apparent and, hence, these soils cannot be classified as Andisols. The major factors determining soil genesis on the island of Thera would appear to be the nature of the parent material and the climate.

Erosion and the Rejuvenation of Weathering-derived Nutrient Supply in an Old Tropical Landscape

Studies of long-term soil and ecosystem development on static geomorphic surfaces show that old soils become depleted in most rock-derived nutrients. As they are depleted, however, static surfaces also are dissected by fluvial erosion. This fluvial erosion leads to colluvial soil transport on the resulting slopes, which in turn can rejuvenate the supply of weathering-derived nutrients to plants. We evaluated the influence of erosion and consequent landscape evolution on nutrient availability along a slope on the Island of Kaua’i, near the oldest, most nutrient-depleted site on a substrate age gradient across the Hawaiian Islands. Noncrystalline minerals characteristic of younger Hawaiian soils increased from 3% of the soil on the static constructional surface at the top of the slope to 13% on the lower slope, and the fraction of soil phosphorus (P) that was occluded (and hence unavailable) decreased from 80% to 56% at midslope. Foliar nitrogen and P concentrations in Metrosideros polymorpha increased from 0.82% and 0.062% to 1.13% and 0.083% on the constructional surface and lower slope, respectively. The increase in foliar P over a horizontal difference of less than 250 m represents nearly half of the total variation in foliar P observed over 4.1 million years of soil and ecosystem development in Hawai’i. The fraction of foliar strontium (Sr) derived from weathering of Hawaiian basalt was determined using 87Sr:86Sr; it increased from less than 6% on the constructional surface to 13% and 31% on lower slope and alluvial positions. Erosional processes increase both nutrient supply on this slope and the fine-scale biogeochemical diversity of this old tropical landscape; it could contribute to the relatively high level of species diversity observed on Kaua’i.

ISOTIC MINERALOGY: CRITERIA REVIEW AND APPLICATION IN BLUE MOUNTAINS, OREGON

The isotic family was established in U.S. Soil Taxonomy to create a division in the mixed mineralogy class identifying soils exhibiting properties of noncrystalline minerals. Application of the isotic class has resulted in correlation problems of soil series in various regions of the country. This study of 56 pedons in the Blue Mountains physiographic province of eastern Oregon examines isotic and andic properties of soils with the following objectives: (i) review theory and background related to the current criteria for the isotic class; (ii) examine these criteria on selected pedons in the Blue Mountains; and (iii) discuss the current approach to the use of the isotic family classification in this geographic region. The criterion, 1500 kPa water retention/clay percentage ≥ 0.6, is derived from the rationale of water adsorbed on surfaces of soil materials and is often used as a criterion for appropriate dispersion during particle-size analysis. The reaction of NaF with noncrystalline soil minerals (e.g., allophane) results in the exchange of hydroxyl ions from the mineral surface with fluoride. The nonlinear increase in pH of NaF establishes the semiquantitative nature of the test. For this study, NaF pH has correlation coefficients of 0.80, 0.72, and 0.34 for acid oxalate-extractable Al, Si, and Fe, respectively. The relationship of NaF pH with properties related to andic materials suggests that different OH sites exist in these soils and that they react at varying rates and release differing amounts of acid oxalate-extractable elements. Calculated clay based on 1500 kPa water retention and using criteria in Soil Taxonomy (2.5 rule) always exceeds measured clay for all horizons. A better relationship of calculated and measured clay was achieved with a factor of 1.7 (rather than 2.5). This factor is derived assuming a linear slope of 0.6 (rather than 0.4) between 1500 kPa water retention and clay. In the Blue Mountains survey area, pedons in the isotic versus mixed families do not correlate with specific geographic areas, moisture/temperature regimes, or parent materials. Lack of mappable differences of these two classes results in no discernible differences in properties affecting interpretations as we currently view them.

Analysis and significance of mineral matter in coal seams

The material described as “mineral matter” in coal encompasses dissolved salts in the pore water and inorganic elements associated with the organic compounds, as well as discrete crystalline and non-crystalline mineral particles. A range of technologies, including but not restricted to low-temperature oxygen-plasma ashing, may be used to evaluate the total proportions of minerals and other inorganic constituents in a coal sample. The relative proportions of the individual minerals in the coal may be further determined by several different techniques, including Rietveld-based X-ray powder diffractometry, computer-controlled scanning electron microscopy (CCSEM), and normative interpretation of chemical analysis data. The mode of occurrence of particular minerals may be evaluated by optical or electron microscopy techniques. The minerals in coal may represent transformed accumulations of biogenic constituents such as phytoliths and skeletal fragments, or they may be of detrital origin, introduced as epiclastic or pyroclastic particles into the peat bed. Other minerals are produced by authigenic precipitation, either syngenetically with peat accumulation or at a later stage in cleats and other pore spaces by epigenetic processes. They may represent solution and reprecipitation products of biogenic and detrital material, or they may be derived from solutions or decaying organic matter within the peat bed. Non-mineral inorganics may be derived from a range of subsurface waters, and possibly redistributed within low-rank seams by post-depositional ion migration effects. They may also be expelled in different ways from the organic matter with rank advance. Quantitative analysis of minerals and other inorganics contributes significantly to defining coal quality. It may also be useful as an aid to stratigraphic correlation, either between seams in a coal-bearing sequence or between sub-sections within an individual coal bed. Mineralogical analysis may help in identifying the mode of occurrence and mobility of particular trace elements, including potentially toxic components such as arsenic and mercury. Knowledge of the mineral matter can also be used to evaluate the behaviour of particular coals in different utilization processes, including the processes that control the characteristics of fly ashes, slags and other combustion by-products.

Carbon Cycling and Soil Carbon Storage in Mesic to Wet Hawaiian Montane Forests

Global surveys have shown that increased precipitation in mesic to wet ecosystems increases soil carbon storage, but it is not clear how changes in water availability act to affect soil carbon since water is generally in excess of plant demand within these humid ecosystems. Differences in precipitation can affect soil carbon storage either by altering the biotic processes involved in carbon cycling or by altering abiotic processes such as carbon adsorption on soil minerals. We compared the relative effect of water on net primary productivity and decomposition, and on soil weathering and mineralogy in controlling soil carbon storage in forests. Patterns of ecosystem carbon cycling and soil carbon storage were measured in Hawaiian montane forest sites similar in temperature regime, parent material, ecosystem age, vegetation, and topographical relief, while mean annual precipitation alone varied from 2200 to >5000 mm/yr. Soil carbon storage ranged from 30.9 to 62.5 kg/m2 and increased by a factor of 1.7 with increased precipitation across the gradient. Neither changes in total secondary minerals nor noncrystalline mineral content could explain increased soil carbon as both decreased with increasing precipitation. Aboveground net primary productivity, soil carbon dioxide flux, and plant litter decomposition rates also decreased with increased precipitation. These data suggest that increased soil carbon storage was not stimulated by an increase in net primary productivity, but instead by a decrease in decomposition rates. Decreased decomposition rates corresponded with low soil reduction–oxidation potentials, suggesting that soil oxygen availability was limiting to microbes. While soil oxygen did not appear to affect plant growth directly, the decline in net primary productivity corresponded with decreased nitrogen availability, a consequence of slower decomposition and nutrient release. Thus, in humid environments the most important effect of variation in water on carbon cycling appears to be its control on the diffusion of oxygen into the soil.

CARBON CYCLING AND SOIL CARBON STORAGE IN MESIC TO WET HAWAIIAN MONTANE FORESTS

Global surveys have shown that increased precipitation in mesic to wet ecosystems increases soil carbon storage, but it is not clear how changes in water availability act to affect soil carbon since water is generally in excess of plant demand within these humid ecosystems. Differences in precipitation can affect soil carbon storage either by altering the biotic processes involved in carbon cycling or by altering abiotic processes such as carbon adsorption on soil minerals. We compared the relative effect of water on net primary productivity and decomposition, and on soil weathering and mineralogy in controlling soil carbon storage in forests. Patterns of ecosystem carbon cycling and soil carbon storage were measured in Hawaiian montane forest sites similar in temperature regime, parent material, ecosystem age, vegetation, and topographical relief, while mean annual precipitation alone varied from 2200 to >5000 mm/yr. Soil carbon storage ranged from 30.9 to 62.5 kg/m2 and increased by a factor of 1.7 with increased precipitation across the gradient. Neither changes in total secondary minerals nor noncrystalline mineral content could explain increased soil carbon as both decreased with increasing precipitation. Aboveground net primary productivity, soil carbon dioxide flux, and plant litter decomposition rates also decreased with increased precipitation. These data suggest that increased soil carbon storage was not stimulated by an increase in net primary productivity, but instead by a decrease in decomposition rates. Decreased decomposition rates corresponded with low soil reduction–oxidation potentials, suggesting that soil oxygen availability was limiting to microbes. While soil oxygen did not appear to affect plant growth directly, the decline in net primary productivity corresponded with decreased nitrogen availability, a consequence of slower decomposition and nutrient release. Thus, in humid environments the most important effect of variation in water on carbon cycling appears to be its control on the diffusion of oxygen into the soil.

Zirkelite from the Sebl'yavr carbonatite complex, Kola Peninsula, Russia: an X-ray and electron microprobe study of a partially metamict mineral

AbstractZirkelite, a cubic mineral of general formula (Ti,Ca,Zr)O2−x occurs as an accessory mineral in phoscorites, carbonatites and associated rocks in the Sebl'yavr complex. After pyrochlore, it is the main mineral concentrating niobium in these rocks. Zirkelite forms platy crystals comprising polysynthetic octahedral twins, often having a complex skeletal internal structure within a cuboctahedral external morphology. The mineral is largely metamict, but after heating to 800°C it produces a cubic crystalline structure with ao = 5.157 ±0.006 Å. It is black to brownish-black in colour, VHN = 760−780 kg.mm−2, density = 4.27 g.cm−3, and reflectance = 12.5%.Chemically, zirkelite is relatively enriched in Nb2O5 (up to 14.5 wt.%) and ThO2 (up to 7.7 wt.%), and it displays four compositionally-distinct zones which probably formed during primary crystallisation processes. It is patchily altered where it is associated with an unidentified Ba, Ti, Nb, Zr silicate phase which partly replaces and pseudomorphs it. Under the current IMA-approved nomenclature scheme, non-crystalline (metamict) minerals of the composition described here would normally be given the general species name zirconolite, with the name zirkelite confined to the cubic mineral. However, at Sebl'yavr, the name zirkelite is used because the mineral displays a well-defined cubic crystal morphology and has a cubic structure after heating.

Weathering and soil forming processes under semi-arid conditions in two Mexican volcanic ash soils

Weathering and neoformation of allophane, imogolite and halloysite in volcanic ash soils have been studied extensively in humid climates but little data are available on these soils in arid and semi-arid conditions. Weathering and soil formation under semi-arid conditions on acid pyroclastics have been investigated in two profiles, both at the micro-site scale and on bulk samples. XR microdiffractions and SEM–EDX microanalysis were performed on soil thin sections. Chemical, particle-size, XRD and mineral identification analysis were performed on conventional soil samples. Results show the interplay of various sub-processes: (a) intense division of the coarse minerals into small fragments 50–200 μm in size; (b) diagenesis of noncrystalline products in the zone of contact with the parent minerals; (c) transformation of noncrystalline minerals into halloysite in the compact soil microstructures and preservation of the noncrystalline minerals in the topsoil; (d) desiccation and condensation of the crystalline and noncrystalline minerals into microaggregates in the topsoil. The results of these interacting weathering processes are silty-loam soils with no cohesion and high susceptibility to wind erosion. Differences appearing between different analytical methods at different sampling scales need special precautions in explaining the results.

Mineral control of soil organic carbon storage and turnover

A large source of uncertainty in present understanding of the global carbon cycle is the distribution and dynamics of the soil organic carbon reservoir. Most of the organic carbon in soils is degraded to inorganic forms slowly, on timescales from centuries to millennia1. Soil minerals are known to play a stabilizing role, but how spatial and temporal variation in soil mineralogy controls the quantity and turnover of long-residence-time organic carbon is not well known2. Here we use radiocarbon analyses to explore interactions between soil mineralogy and soil organic carbon along two natural gradients—of soil-age and of climate—in volcanic soil environments. During the first ∼150,000 years of soil development, the volcanic parent material weathered to metastable, non-crystalline minerals. Thereafter, the amount of non-crystalline minerals declined, and more stable crystalline minerals accumulated. Soil organic carbon content followed a similar trend, accumulating to a maximum after 150,000 years, and then decreasing by 50% over the next four million years. A positive relationship between non-crystalline minerals and organic carbon was also observed in soils through the climate gradient, indicating that the accumulation and subsequent loss of organic matter were largely driven by changes in the millennial scale cycling of mineral-stabilized carbon, rather than by changes in the amount of fast-cycling organic matter or in net primary productivity. Soil mineralogy is therefore important in determining the quantity of organic carbon stored in soil, its turnover time, and atmosphere–ecosystem carbon fluxes during long-term soil development; this conclusion should be generalizable at least to other humid environments.

The CaO distribution to mineral phases in a high calcium fly ash from Eastern Germany

High Calcium Fly Ashes (HCFA) are increasingly important as an admixture to mortar and concrete. The reactivity of HCFA is related to mineral phases like free lime, glassy spheres, anhydrite and yee'liminite. The occurrence of CaO in several crystalline phases and at least one non-crystalline mineral phase complicates the quantification of any of those mineral phases. This study focuses on an direct assessment of free lime and an indirect method for determination of CaO bounded in glassy spheres and anhydrite. CaO is enriched in fine particle size ranges. Glassy spheres are the most important CaO bearing mineral phase in the examined HCFA. The maximum CaO content bound in a glassy matrix is close to the composition of anorthite (< 25 wt%). This is probably due to the restricted solubility of chemical species in a cooling melt of anorthitic composition. At the end of the high temperature process an equilibrium is attained between free lime, anhydrite and glassy spheres. The distribution of CaO among mineral phases is controlled by the availability of SO 3 and free lime.

Noncrystalline Fe-Si-Al-Oxyhydroxides

AbstractHigh-resolution transmission electron microscopy of noncrystalline Fe-Si-Al-oxyhydroxide gels shows a common structure of hollow packed spheres having external diameters ranging from 50 to 1000 Å. Some sphere walls display a concentric structure, particularly if the gel composition is close to that of a crystalline clay mineral (e.g., smectite, kaolin). The spheres probably formed by expansion of void space (bubbles) as the surrounding gel contracted 5–10% because of partial ordering of the Fe-Si-Al-oxygen network. Much of the water contained in such noncrystalline minerals is incorporated within the bubbles.

軽視されてきた鉱物 非晶質鉱物・土壌たい積物研究上での重要性

Non-crystalline mineral components of soils and sediments have great influence on their physical, chemical and biological properties. These, because the components possess large surface area, are often reagents for cementing and coating surfaces of crystalline particles and change their own reactivities depending on the pH of system involved. In contrast with the striking progress in research of crystalline minerals, studies for non-crystalline minerals have reluctantly been neglected. There is very limited knowledge for their characterization. In this article, several problems encountered due to the lack of knowledge were presented by examples from the studies of Canadian soil minerals. The necessity of basic research was emphasized to gain better understanding of such components.

Structure and function of bone collagen fibrils

The intermolecular volume of fully hydrated collagen fibrils from a number of mineralized and non-mineralized tissues of adult rats has been determined both by an exclusion technique and by a method which involves the monitoring of specific X-ray diffraction parameters. The intermolecular volume of either bone or dentinal fibrils is approximately twice that of either tail or achilles tendon, and the most frequent intermolecular distance in bone or dentine fibrils is approximately 3 Å larger than of the tendons. A number of fibrillar structures are most compatible with the intermolecular volume of rat tail tendon. These include hexagonal molecular packing and orthogonal arrays of microfibrils comprising seven parallel molecular strands. The intermolecular volume of bone or dentinal collagen fibrils, on the other hand, appears to arise from structures having a disordered or pseudo-hexagonal molecular packing, in which the most frequent intermolecular distance is about 19 Å. The space associated with collagen fibrils in adult bone is such that 70 to 80% of the mineral is located within the intermolecular space of the fibrils—approximately equal amounts of mineral being in spaces having lateral dimensions of 25 to 75 Å and 6 to 12 Å, respectively. Particles located in the latter kind of intermolecular space probably constitute, to a large extent, the non-crystalline mineral phase of adult bone. The stereo-chemical constraints on the transport of mineral ions into and within collagen fibrils of bone and tendon support the postulate that bone collagen is an in vivo catalyst for mineral deposition and further suggests that its catalytic activity may be partially regulated through its molecular packing.