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1.
Weathering and weathering rates of natural stone   总被引：3，自引：0，他引：3  
Physical and chemical weathering were studied as separate processes in the past. Recent research, however, shows that most processes are physicochemical in nature. The rates at which calcite and silica weather by dissolution are dependent on the regional and local climatic environment. The weathering of silicate rocks leaves discolored margins and rinds, a function of the rocks' permeability and of the climatic parameters. Salt action, the greatest disruptive factor, is complex and not yet fully understood in all its phases, but some of the causes of disruption are crystallization pressure, hydration pressure, and hygroscopic attraction of excess moisture. The decay of marble is complex, an interaction between disolution, crack-corrosion, and expansion-contraction cycies triggered by the release of residual stresses. Thin spalls of granites commonly found near the street level of buildings are generally caused by a combination of stress relief and salt action. To study and determine weathering rates of a variety of commercial stones, the National Bureau of Standards erected a Stone Exposure Test Wall in 1948. Of the many types of stone represented, only a few fossiliferous limestones permit a valid measurement of surface reduction in a polluted urban environment.  相似文献   

2.
Weathering rinds formed in Mesozoic sandstone and basalt cobbles buried in terrace deposits for up to 300 ka have been investigated. The aim was to determine the formation process and elemental mass balances during rind development. The ages of terraces distributed in the western part of Fukui prefecture, central Japan have been determined as 50 ka, 120 ka and 300 ka based on a tephro-stratigraphic method. Detailed investigations across the weathering rinds, consisting of microscopic observations, porosity measurements, and mineralogical and geochemical analyses using X-ray diffractometry (XRD), X-ray fluorescence (XRF), secondary X-ray analytical microscopy (SXAM), scanning electron microanalyser (SEM) and electron probe microanalysis (EPMA) have been carried out. The results revealed that the Fe concentrations in the weathering rind of a basalt cobble slightly decreased from the cobble’s surface (rim) towards the unweathered core. In contrast, in a sandstone cobble formed under the same environmental conditions over the same period of time there is an Fe-rich layer at some distance below the cobble’s surface. Elemental mass balances across the rinds were determined by using open system mass balance (τi,j) calculations and show that the Fe was precipitated as Fe-oxyhydroxides in the basalt cobbles, although Fe was slightly removed from the rims. In sandstone cobbles, on the other hand, Fe migrated along a Fe concentration gradient by diffusion and precipitated as Fe-oxyhydroxide minerals to form the weathering rinds. Presumably, precipitation was due to the relatively higher pH conditions caused by mineral dissolution within the pores, principally involving calcite, but probably also silicates including feldspar. The detailed characterization of the weathering rinds revealed the influence of lithology on the accumulation and dissolution of Fe-oxyhydroxides, causing weathering rinds with different characteristics to develop in different kinds of buried cobbles under the same conditions. Relatively large climatic changes in the study area did not cause discernable variations in the mean formation rates of the studied rinds, which were in the order of 10?8 m/a for both basalt and sandstone cobbles. These rates are 1–2 orders of magnitude slower than those reported for tropical areas elsewhere, most probably due to the lower rainfall in the studied area.  相似文献   

3.
Weathering of volcanic tuff rocks caused by moisture expansion   总被引：1，自引：1，他引：0  
Moisture expansion in natural building stones is considered one of the most important factors affecting their weathering and deterioration. The processes that may be responsible for the expansion under determinate relative humidity (hygric dilatation) and water-saturated conditions (hydric dilatation) are generally attributed to the presence of swellable clay minerals. In contrast to this assumption, our investigations show that moisture expansion also takes place in volcanic tuff building stones almost free from clay minerals. To provide a deeper understanding of the processes, swelling and deterioration were performed on 14 volcanic tuffs used as important building stones of different ages, compositions and weathering stages from Mexico, Germany and Hungary. The investigations undertaken include extensive chemical, petrophysical and fabric analyses. The samples show a wide range of effective porosity, microporosity, capillary water absorption, moisture expansion, and CEC values. High moisture expansion does not seem to depend on clay mineral content alone. We also observed that there is no significant effect on dilatation if clay minerals are present but only form a thin coat on the outer shell of bigger pores. Moreover, we identified a correlation between microporosity, average pore radius and moisture expansion. The investigations highlight the fact that moisture expansion cannot only be attributed to swellable clay minerals, and suggest that the presence and accumulation of micropores and their average radius and distribution play an important role for non-clay associated swelling intensity, which can most probably be attributed to the disjoining pressure.  相似文献   

4.
The exposed crust consists mainly of plagioclase (35%), quartz (20%), K-feldspar (11%), volcanic glass (12%), biotite (8%), and muscovite (5%). Quartz is a resistate, thus feldspars and glass represent approximately 75 percent of the labile minerals. The weathering characteristics of these constituents are summarized in the context of thermodynamic, mass balance and kinetic considerations.Experimentally determined release rate constants were used to predict the proportions of Ca, Na and K released by feldspars of plutonic rocks (granites to gabbros) to weathering solutions. The chemical weathering trends of the weathered residues, calculated from the kinetic data, conform closely to the initial trends observed in some recent weathering profiles, demonstrating the accuracy of the predictions. Since the weathering of feldspars is controlled by processes that should not change through geological time, the relative release rates of Ca, Na, and K from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering.Experimentally determined release rate constants are not available for a wide range of volcanic glass compositions, but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks. The kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile.  相似文献   

5.
刘再华 《地球学报》2001,22(5):477-480
CO2向H^ 和HCO3^－的转换是一相对慢速过程。因此，其动力学可能决定碳酸盐岩的溶解速率。在灰岩和白云岩的溶解实验中，使用了自然界普遍存在的碳酸酐酶（CA）来催化这一CO2转换反应，结果发现，对灰岩而言，加入CA后，其溶解速率在高CO2分层时可增加10倍，而对白云岩，其溶解速率增加主要在低CO2分压时，可达3倍左右。这一发现表明，化学风化（包括碳酸盐岩溶解和硅酸盐风化）作用在大气CO2沉降和全球碳循环里的所谓丢失的汇中的重要性需要重新评价。毫无疑问，已往的研究由于未认识到CA在风化中的催化作用，因此低估了风化作用的速率，同时也低估了风化作用对大气CO2沉降的贡献。另一方面，也表明了研究自然界不同水体中CA分布及其活度和CA在自然界风化作用中的作用的必要性。  相似文献   

6.
Recent work on the weathering of high standing islands (HSI’s) of New Zealand (Goldsmith et al., 2008), Dominica (Goldsmith et al., 2010) Martinique and Guadeloupe (Rad et al., 2006) and portions of the Philippines (Schopka et al., 2011) shows weathering rates based on stream water chemistry for areas draining andesitic terrains are comparable to weathering rates determined for basaltic terrains, indicating that andesite weathering might be much more important in drawing down atmospheric CO2 than previously recognized. While an easily erodible parent material has been largely attributed to sustaining rates at these locations, little is known to known regarding its associated reaction kinetics. We conducted a series of batch dissolution experiments on andesitic material collected from ∼10,000 year old tephra deposits from Dominica to determine the dissolution rate of major and trace mineral phases to better understand geochemical processes controlling weathering flux from these areas. Dissolution experiments were conducted over a range of pH (4 and 7) on bulk samples and mineral separates.The dissolution rates based on Si release from the Dominica tephra bulk samples were similar, and ranged from 0.04 to 0.13 μmole Si/g-day in water, and ∼0.14 to 0.27 μmole Si/g-day in dilute acid (initial pH ∼4). Although the bulk of the ash is predominately composed of vesicular felsic (Na–Al–Si) volcanic glass, reaction rates and stoichiometry indicate ash dissolution is dominated by the reactivity of trace Mg or Ca-bearing silicate phases (olivine, pyroxene or amphiboles) and Ca–phosphate phases (apatite), especially under slightly acidic conditions. Analysis of reacted phases by SEM shows little evidence of alteration of glassy material, whereas surfaces of Ca–Mg inosilicates, olivine and apatite show etched features indicative of dissolution. Results of the dissolution experiments suggest that, although these phases are relatively minor components of the ash, they contribute disproportionately to the overall weathering flux, and their reactivity may be particularly important in areas where physical weathering and erosion are constantly exposing new fresh surfaces available for chemical reaction.  相似文献   

7.
火山熔岩油气藏是准噶尔盆地油气勘探和开发的重要目标之一。通过对准噶尔盆地西泉地区16口石炭系火山熔岩井的岩心观察、普通薄片和铸体薄片镜下鉴定和定量统计、扫描电镜和X-射线衍射等实验,研究玄武岩、安山岩、英安岩的岩石学特征、孔隙类型及储集特征及异同点,建立火山熔岩成岩演化序列,探讨成岩作用对火山熔岩孔隙演化的影响。研究表明,安山岩的储集空间最发育,孔隙类型及组合多样,多为气孔+斑晶溶孔+基质溶孔+溶蚀缝组合和气孔+斑晶溶孔+基质溶孔+溶蚀缝+构造裂缝组合。英安岩的孔隙组合为气孔+斑晶溶孔+基质溶孔和气孔+斑晶溶孔+基质溶孔+溶蚀缝。玄武岩孔隙类型及组合单一,为构造裂缝+溶蚀缝,构造裂缝+基质溶孔,气孔+溶蚀缝。挥发分逸出作用控制火山熔岩原生气孔的发育,岩浆期后热液作用和充填作用破坏了火山熔岩的储集空间,溶蚀作用、风化淋滤作用和构造破裂作用极大地改善了火山熔岩的储集性能。认为西泉地区石炭系顶部风化剥蚀淋滤带(距石炭系顶面0～20 m)的安山岩是油气聚集的最有利层段。  相似文献   

8.
Volcanic areas play a key role in the input of elements into the ocean and in the regulation of the geological carbon cycle. The aim of this study is to investigate the budget of silicate weathering in an active volcanic area. We compared the fluxes of the two major weathering regimes occurring at low temperature in soils and at high temperature in the active volcanic arc of Kamchatka, respectively. The volcanic activity, by inducing geothermal circulation and releasing gases to the surface, produces extreme conditions in which intense water-rock interactions occur and may have a strong impact on the weathering budgets. Our results show that the chemical composition of the Kamchatka river water is controlled by surface low-temperature weathering, atmospheric input and, in some limited cases, strongly imprinted by high-temperature water-rock reactions. We have determined the contribution of each source and calculated the rates of CO2 consumption and chemical weathering resulting from low and high-temperature water/rock interactions. The weathering rates (between 7 and 13.7 t/km2/yr for cations only) and atmospheric CO2 consumption rates (∼0.33-0.46 × 106 mol/km2/yr for Kamchatka River) due to rock weathering in soils (low-temperature) are entirely consistent with the previously published global weathering laws relating weathering rates of basalts with runoff and temperature. In the Kamchatka River, CO2 consumption derived from hydrothermal activity represents about 11% of the total HCO3 flux exported by the river. The high-temperature weathering process explains 25% of the total cationic weathering rate in the Kamchatka River. Although in the rivers non-affected by hydrothermal activity, the main weathering agent is carbonic acid (reflected in the abundance of in rivers), in the region most impacted by hydrothermalism, the protons responsible for minerals dissolution are provided not only by carbonic acid, but also by sulphuric and hydrochloric acid. A clear increase of weathering rates in rivers impacted by sulphuric acid can be observed. In the Kamchatka River, 19% of cations are released by hydrothermal acids or the oxidative weathering of sulphur minerals.Our results emphasise the important impact of both low and high-temperature weathering of volcanic rocks on global weathering fluxes to the ocean. Our results also show that besides carbonic acid derived from atmospheric CO2, hydrochloric acid and especially sulphuric acid are important weathering agents. Clearly, sulphuric acid, with hydrothermal activity, are key parameters that cause first-order increases of the chemical weathering rates in volcanic areas. In these areas, accurate determination of weathering budgets in volcanic area will require to better quantify sulphuric acid impact.  相似文献   

9.
The conversion of CO2 into H+ and is a relatively slow reaction. Hence, its kinetics may be rate determiningin carbonate rock dissolution. Carbonic anhydrase (CA), which is widespread in nature, was used to catalyze the CO2 conversion process in dissolution experiments of limestone and dolomite. It was found that the rate of dissolution increases by a factor of about 10 after the addition of CA at a high CO2 partial pressure (Pco2) for limestone and about 3 at low Pcoj for dolomite. This shows that reappraisal is necessary for the importance of chemical weathering (including carbonate rock dissolution and silicate weathering) in the atmospheric CO2 sink and the mysterious missing sink in carbon cycling. It is doubtless that previous studies of weathering underestimated weathering rates due to the ignorance of CA as an activator in weathering, thus the contribution of weathering to the atmospheric CO2 sink is also underestimated. This finding also shows the need to examine the situ distribution and activ  相似文献   

10.
This paper reports novel data concerning the volcanic formation of the Piperno, a stone that has been used for a long time in the monumental architecture of Naples and the Campanian region (Southern Italy). A careful field survey of the outcrops or underground sites so far accessible allowed us to draw a lithostratigraphic reconstruction of the formation and enabled the recognition of the three main layers exploited in past centuries and which provided dimension stones for architectural and structural purposes. Petrophysical and mineralogical characterization also enabled us to discriminate the same layers previously identified. Different scoriae/matrix ratio, scoriae dimension and welding degree are the most peculiar features of these horizons. The combination of these three parameters, even though they did not affect the use of Piperno as dimension stone, somehow determined its variable susceptibility to the weathering agents. However, a linear relationship between the exposure time and the decay of the stone itself, at a parity of weathering intensity, was not observed. This assumption was proved by verifying that the specific layers of the volcanic sequence controlled the weathering degree of Piperno from monuments disregarding their age of emplacement.  相似文献   

11.
The Lesser Antilles have very high chemical weathering rates, with values that can reach 1290 t/km2/a. The tropical environment induces high precipitation rates, high temperature, dense vegetation, with sharp relief and thick soils. Because of volcanic activity, frequent pyroclastic flows produce very erodible and porous materials. In addition, agriculture induces important land use changes which replace existing native forest cover with banana and sugar cane plantations. Their surface can cover as much as 40% of the total area of a river basin. The aim of this study is to identify key parameters, either natural or anthropogenic, that control chemical weathering rates. Among the combined impact of all parameters (climate, runoff, slopes, vegetation etc.), basin age seems to be the control parameter: the younger the basin, the higher the weathering rate. A correlation between the chemical weathering rate and the basin age suggests that young volcanic rocks are more easily weathered than old ones: young fresh material is easily mobilized by erosion, while for older rocks with thick soil covers, chemical rates are much lower. A combined effect between the higher erodibility and a higher climate erosivity of the younger relief could be observed. Moreover, a correlation between banana plantations and the chemical weathering rates that can be explained by an increase of infiltration, due to stem flow processes is shown here. Banana plantations also have a correlation with the basin age, older basins being more favorable terrains for cultivation.  相似文献   

12.
Groundwater qualities of coastal aquifers in the Ottapidaram taluk of Thoothukudi district, Tamil Nadu have been extensively monitored in post monsoon seasons in 2014 to assess its suitability in relation to domestic and drinking uses in four regions (N-S-EW). 34 groundwater samples were analyzed for various physicochemical attributes like pH, electrical conductivity (EC), Total dissolved solid (TDS), Na, K, Ca, Mg, Cl, HCO3, CO3, SO4, NO3, PO4. Most of these parameters fall under not permissible limits. The western part of the study area is highly polluted from K, Cl, HCO3 due to industrial/agriculture activity. The southern part is less polluted compared to other region. Hydrogeochemical processes controlling the water chemistry (Gibbs) indicates that most of groundwater samples fall at rock-weathering supremacy zone. Geochemical processes and temporal variation in the groundwater in this area are influenced by evaporation processes, ion exchange and dissolution of minerals. Major cation and anion ionic interaction indicate that weathering reactions have an inconsequential role in the hydrochemical processes of the shallow groundwater system. As a result of the hydrogeochemical analysis, seawater intrusion, aquifer rock weathering, sewer leakage are the overriding factors that determine the major ionic composition. The appropriate management plan is necessary to preserve precious groundwater resources.  相似文献   

13.
Quaternary alkaline basalts of Middle Atlas, are weathered into spheroidal volumes organized into weathering cover. In the profile studied, the study of transformations from a fresh core basalt to the most weathered rinds, has been analysed using BESI images (backscattred electron image analysis). A part from the microscopic analysis of each weatherted basalt, proportions of primary minerals, clays and pore space has been quantified in different stages of weathering. Indeed, in fresh core basalt, weathering is characterized by a first dissolution of the glass, followed by feldspar transformations in twinning plans, cleavages and in micropores inherited from the magmatic and cristallographic history of the rock.

In most basaltic weathered rinds, pore spaces given by the dissolution of the glass, were filled by a mixture of clays and iron products. In these samples, feldspars are completely dissolved giving important porosity occupied by small quantity of halloysite and kaolinite. The olivine and pyroxene transformations are accompanied by weak pore space formation. At the bottom of the soil, this porosity decreases in response to filling by later secondary products which come from the upper part of the soil by weathering solutions.  相似文献   


14.
岩体化学风化的非连续性及其科学意义   总被引：5，自引：0，他引：5  
岩体化学风化在空间上具有高度的非连续性,这种非连续性广泛存在于从宏观、细观到微观的所有尺度。宏观结构面是化学风化最主要的发生场所;风化岩体内,新鲜岩块被沿结构面内法线方向发育的腐蚀带包围,呈斑点状分散于腐岩中。微缝等细观损伤普遍存在于各类岩石中;化学风化从岩块内不同空间位置的水力有效空隙向三维空间扩展,决定了细观尺度上化学风化的非连续性。矿物溶解是在晶体中具有过剩表面能的缺陷位置优先发生的,因而具有显著的微观非连续性。由于非连续特性,化学风化可增大水岩界面,提升矿物溶解反应的规模及速率。通过对既有损伤的扩展及在损伤空间堆积残余物,化学风化具有分离—裂化岩体、岩块及造岩矿物的重要作用,这种作用可使以新鲜岩石为主的岩体大规模脱离母岩,而堆积于坡脚的岩石块体在化学风化的继续作用下,可裂解为更小的岩屑或矿物碎屑,为向水体搬运创造条件,从而极大地促进斜坡夷平及地貌重塑进程。  相似文献   

15.
Detailed mineral and chemical studies of samples of syenite rocks with thick weathering rinds, found in the alkaline massifs on Ilha de São Sebastião, illustrate the complex interplay between variables controlling initial weathering processes. An array of geochemical information was obtained by optical and electron microscopy, X-ray analyses, mass spectroscopy and optical spectrometry. Sericite and metahalloysite are the principal phases nucleating and forming as the perthitic feldspar rock matrix disintegrates. Incipient feldspar dissolution and the formation of submicrometer X-ray opaque secondary phases were observed in “fresh rock” material using transmission electron microscopy. Pore waters, from which secondary phases nucleate and grow are under the constant influence, as alteration proceeds, of physical (e.g., accessibility of mineral surfaces to percolating fluids) and chemical (e.g. chemistry of minerals providing the dominant solutes) controls. Minor- and trace-element signatures do not vary significantly except for Zn, Rb, Sr, Y, REE and Pb. Lathanide mobilities appear related to their host-mineral stabilities with respect to ambient pore waters.  相似文献   

16.
关于岩石风化过程中化学组分迁移的定量研究方法   总被引：9，自引：0，他引：9  
岩石化学分析结果的定和效应给定量研究风化体系中化学组分的迁移规律带来困难。一般岩石风化体系可以有母岩-滤液和母岩-风化产物两个子体系。本文即探讨该二子体系中化学组分迁移的定量计算问题。对比分析表明,母岩-滤液子体系方法较适用于风化程度高的体系,而母岩-风化产物子体系方法较适用于风化程度低的体系。对于风化程度中等的体系,宜采用两种子体系方法所得结果的加权平均,其中权重按风化程度取值。  相似文献   

17.
Chemical weathering of silicate minerals consumes atmospheric CO2 and is a fundamental component of geochemical cycles and of the climate system on long timescales. Artificial acceleration of such weathering (“enhanced weathering”) has recently been proposed as a method of mitigating anthropogenic climate change, by adding fine-grained silicate materials to continental surfaces. The efficacy of such intervention in the carbon cycle strongly depends on the mineral dissolution rates that occur, but these rates remain uncertain. Dissolution rates determined from catchment scale investigations are generally several orders of magnitude slower than those predicted from kinetic information derived from laboratory studies. Here we present results from laboratory flow-through dissolution experiments which seek to bridge this observational discrepancy by using columns of soil returned to the laboratory from a field site. We constrain the dissolution rate of olivine added to the top of one of these columns, while maintaining much of the complexity inherent in the soil environment. Continual addition of water to the top of the soil columns, and analysis of elemental composition of waters exiting at the base was conducted for a period of five months, and the solid and leachable composition of the soils was also assessed before and after the experiments. Chemical results indicate clear release of Mg2+ from the dissolution of olivine and, by comparison with a control case, allow the rate of olivine dissolution to be estimated between 10−16.4 and 10−15.5 moles(Mg) cm−2 s−1. Measurements also allow secondary mineral formation in the soil to be assessed, and suggest that no significant secondary uptake of Mg2+ has occurred. The olivine dissolution rates are intermediate between those of pure laboratory and field studies and provide a useful constraint on weathering processes in natural environments, such as during soil profile deepening or the addition of mineral dust or volcanic ash to soils surfaces. The dissolution rates also provide critical information for the assessment of enhanced weathering including the expected surface-area and energy requirements.  相似文献   

18.
模拟不同气候条件下碳酸盐岩风化作用的淋溶实验研究   总被引：3，自引：3，他引：0  
通过模拟干热、湿热与干冷3种气候条件,以饱和CO2水作为淋溶液,对黔中岩溶区3条碳酸盐岩风化壳岩-土界面的岩粉层试样进行了淋溶实验(其中干热、湿热条件下淋溶到残余酸不溶物阶段),对淋出液的pH值以及主要造岩元素的浓度进行了动态分析。结果表明,碳酸盐岩风化壳岩-土界面由岩到土的转变过程中,伴随碳酸盐的溶蚀,酸不溶物已表现出明显的风化倾向。碳酸盐的溶蚀强度表现为干冷>干热>湿热的变化趋势。温度低,碳酸盐的溶解速率大;排水条件好,碳酸盐溶解释放的Ca、Mg易随风化流体排出体系。对于酸不溶物组分,淋溶实验中有:(1)K、Na、Mg、Si、P的载体矿物风化强度在干热条件下最大(至于Ca,由于方解石与白云石均是其主要的载体矿物,酸不溶物相中的Ca难以在淋出液中有效识别)。在干冷与湿热之间,K、Na、Mg等盐基离子的溶出能力大多表现为湿热>干冷,指示了温度对盐基离子释放强度的重要制约作用;而Si和P未表现出一致的变化趋势,可能源于淋溶体系微环境的差异。(2)Fe与Mn表现出弱迁移性。其中,Fe在干冷环境下淋出强度最弱,说明温度是制约含Fe矿物分解速率的重要因素。而Fe在干热与湿热之间,以及Mn在3种淋溶条件下,未呈现出一致的变化趋势。(3)Al和Ti在碳酸盐岩风化过程中表现出强烈的惰性。   相似文献   

19.
Anthropogenic and natural climate change affect processes in the atmosphere, biosphere, hydrosphere, and pedosphere. The impact of climate on soil evolution has not been well-explored, largely due to slow rates and the complexity of coupled processes that must be observed and simulated. The rates of mineral weathering in loess deposited 23 kyr ago and experiencing soil formation for 13 kyr are explored here using the WITCH model for weathering and the GENESIS model for climate simulation. The WITCH model, which uses rigorous kinetic parameters and laws with provision for the effect on rates of deviation from equilibrium, can successfully simulate the depletion profiles in the soil for dolomite and albite if soil CO2 is assumed to rise over the last 10 kyr up to about 30-40× the present atmospheric pressure, and if the solubility product of the Ca-smectite is assumed equal to that of an Fe(III)-rich Ca-montmorillonite. Such simulations document that dissolution behavior for silicates and carbonates are strongly coupled through pH, and for Ca-smectite and feldspars through dissolved silica. Such coupling is not incorporated in simple geometric and analytical models describing mineral dissolution, and therefore probably contributes to the long-standing observation of discrepancies among laboratory and field mineral dissolution rates.  相似文献   

20.
We hypothesize that the weathering of building stones can be attributed to surface dissolution processes. We assume that chemical interactions occur on grain boundaries and/or microcracks and that diffusion is the controlling process. A dissolution layer (rind) develops adjacent to the weathering surface. We quantify the extent of dissolution by introducing a damage variable f; f=0 for pristine rock, and when f=1 the rock disintegrates. We assume that the variations of the damage variable are given by the diffusion equation. We solve two problems. The first is for the structure of the transient dissolution boundary layer prior to surface disintegration. We find an incubation time ti, before active weathering (disintegration) begins. The second is the solution for steady-state weathering with a constant weathering velocity vw. Our results are entirely consistent with weathering studies on Carrara marble gravestones in the United Kingdom. Typical incubation times are ti=20–30 years, and typical steady-state weathering velocities are vw=5–50 m year–1.  相似文献   

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