The effect of pH and salty solutions on durability of sandstones of the Aghajari Formation in Khouzestan province,southwest of Iran

Slake durability of rocks is a vital engineering geological property of rock materials that has an important role in the promotion of slope stability, evaluation of rock materials, as well as the estimation of stone degradability. This parameter is related to such factors as mineralogy, physical characteristics of rocks, and the environmental conditions. A major part of south and southwestern Iran embraces the Aghajari Formation whose sandstones are used to form the foundations for some structures in Khouzestan province where they are being extensively used as aggregate(s). In this paper, tests of mineralogical examinations, physical properties, and slake durability of sandstones from Ahwaz and Haftkel anticlines were administered in order to assess the durability and degradability of these rocks. The rock durability of each type was evaluated to be up to 15 cycles in acidic and alkaline watery environments and salt aqueous solutions. The results showed that durability of sandstones under study is related to their petrographical and physical characteristics. The durability index of the sandstone samples was decreased by pH reduction and by increasing the concentration of aqueous solutions. The durability index of Ahwaz samples, too, was decreased in basic solutions while this index increased for Haftkel sandstones with the increase in the pH of solutions. Also, the obtained results illustrated that durability index decreased with the increase in the number of cycles. Based on the results, all sandstones show that the durability in sodium sulfate solution is much lower than that for the sodium chloride. Moreover, the slake durability index of the sandstones is decreased with an increase in the concentration of aqueous solutions. As a final statement, the Ahwaz sandstones show lower resistance to weathering processes than Haftkel sandstones; therefore, the use of rocks as building stones is not recommended here.     

Geotechnical and mineralogical properties of weak rocks from Central Greece

Thirty bulk samples of hard soils-soft rocks such as marls, originating from Euboea Island and Peloponnesus area, were investigated to evaluate their geotechnical behavior. Specifically, by conducting a series of physical and geotechnical tests, such as liquid limit and plastic limit tests, along with the estimation of the grain size fraction, Slake Durability and Point Load Test. Certain parameters were determined and used for empirical correlations with their mineralogical characteristics. The mineralogical composition was determined by X-ray diffraction, thermo-gravimetric and thermal analysis, succeeded by textural analysis performed by Optical Microscope. With the help of the above mentioned tests, we interpreted the observed geotechnical behavior of the examined weak rocks by means of mineralogical composition and texture. Durability and the unconfined compressive strength was found to be influenced by high percentages in carbonate minerals. In addition, it was found that a decrease in clay content resulted in higher strength and durability values. The concluded empirical correlations verified the influence of these parameters and gave a general overview of the engineering behavior of the examined weak rocks.     

Factors affecting the durability of selected weak and clay-bearing rocks from Turkey, with particular emphasis on the influence of the number of drying and wetting cycles

Weathering can induce a rapid change of rock material from initial rock-like properties to soil-like properties. The resistance of a rock to short-term weathering is described through a durability parameter called the slake durability index. As durability is an important engineering parameter, particularly for weak and clay-bearing rocks, it was assessed by a number of tests. The main purpose of this study is to assess the influence of the number of drying and wetting cycles and controls of mineralogical composition and strength on durability. For this purpose, 141 samples of different types of weak and clay-bearing rocks were selected from different parts of Turkey, and relationships between the above-mentioned rock characteristics were statistically investigated. The samples were subjected to multiple-cycle slake durability testing, X-ray diffraction (XRD) analysis and uniaxial compression testing. In addition, to assess the influence of mineralogical composition on durability, the mineral contents of the original material and the material passing from the drum of the slake durability apparatus after each cycle were also determined by XRD. The results indicate that the type and amount of clay minerals are the main factors influencing the variations of the slake durability index in all samples. The durability of the clay-bearing rocks studied correlates best with the amount of expandable clay minerals. A strong relationship between the uniaxial compressive strength and the fourth-cycle slake durability index is found only for the marls among the rock types studied. Assessment of gradation results of the spoil pile materials consisting of clay-bearing rocks also reveals that the increase in percentage of fines in old piles is indicative of material degradation, as is evident by multiple-cycle slaking. It is emphasized that two-cycle conventional slake durability testing did not appear to offer an acceptable indication of the durability of weak and clay-bearing rocks when compared with multiple-cyclic wetting and drying. Comments on the performance of the test are made that aim to make the testing process and interpretation of the results more reliable.     

Slaking durability and its effect on the doline formation in the gypsum

Texture and grain size is of great importance in understanding the mechanical properties of rocks. The aim of this study was to investigate textural and slaking durability characteristics, and correlate them with the gypsum types where the dolines occurred, with particular reference to the texture and crystal size. The investigation comprised two stages: field work and laboratory testing. Initially, rock samples were obtained from various representative karstified and non-karstified locations. Thereafter, mineralogical, physical and slaking durability characteristics of the gypsum samples were determined by means of laboratory testing. After the field and laboratory works, the geological, mineralogical and slaking durability characteristics of the study area gypsum were reviewed and discussed from the point of view of doline formation. Results showed that fine grain sized alabastrine gypsum tends to be karstified and leads to doline formation. This is closely related to the crystal size, texture and attributable to the slaking durability of the gypsum. Consequently, the results demonstrate that the texture, especially crystal size, and effective porosity are important parameters controlling the slake durability of the gypsum and doline formation.     

Slake durability and mineralogical properties of some pyroclastic and sedimentary rocks

Slake durability of rocks is an important property of rock-mass and rock-materials in geotechnical practice. The slake durability of rocks is closely related to their mineralogical composition. In this paper, mineralogical examinations and slake durability tests for argillaceous clastic rocks, especially pyroclastic rocks, sandstones and mudstones of Neogene Tertiary age from Japan, were performed in order to assess the slake durability and rock alteration process of these rocks as well as to understand the relationship between mineralogy and durability.The mineral composition and textural features of the rocks were studied by means of optical microscopy (OM), X-ray diffractometry (XRD), electron microprobe analysis (EPMA), and scanning electron microscopy (SEM). In addition, the slake durability test was carried out by using the standard testing method of ISRM [Int. J. Rock Mech. Min. Sci. 16 (1979) 148] in distilled water and in the aqueous solutions with dissolved electrolytes of NaCl and CaCl₂.The pyroclastic rocks and tuffaceous sandstone, rich in di-octahedral and tri-octahedral Fe smectite, respectively, show distinctively different slaking behaviors. The pyroclastic rocks show relatively high slaking (Id₂=55.5% and Id₁₀=10.5%) than the tuffaceous sandstone (Id₂=94.1% and Id₁₀=87.8%, refer to text for Id₂ and Id₁₀). This difference in the slake durability observed in these rocks is due to the microscopic occurrences of smectite present in the interspaces between the particles (pyroclastic rocks) and zeolite cementing the interspaces (tuffaceous sandstone) as alteration minerals. In addition, the durability results of tuffaceous sandstone show that the slake durability decreases as the degree of weathering increases (weathered material Id₂=88.7% and Id₁₀=65.3%). Furthermore, two mudstones of Miocene and Pliocene ages, having different clay mineral compositions (smectite vs. illite+chlorite), show the lowest and the highest slake durability among the tested clastic rocks. Hard mudstone shows the highest (Id₂=98.1% and Id₁₀=95.5%) while the soft mudstone shows the lowest (Id₂=33.9% and Id₆=0.4%.) slake durability. Thus, the slake durability of pyroclastic and sedimentary rocks is greatly affected by their mineral composition and texture, and is closely related to their alteration history. Slake durability is also affected by the kind of dissolved electrolyte and its concentration in the aqueous solution, providing some useful information for geotechnical practice.     

碳酸盐岩红色风化壳中的氧化铁矿物

氧化铁矿物是碳酸盐岩红色风化壳的主要矿物成分和重要结构单元。运用X射线衍射、透射电镜、扫描电镜、穆斯堡尔谱和电子探针等方法对碳酸盐岩红色风化壳中的氧化铁矿物进行了系统研究。碳酸盐岩红色风化壳中的氧化铁矿物主要有针铁矿、赤铁矿和磁赤铁矿。氧化铁矿物组合、含量和化学成分随成土环境和风化强度在剖面中呈明显的规律性变化,这为碳酸盐岩风化成土作用、红色风化壳成因与环境问题的深入研究提供了重要的矿物学依据。     

西藏申扎县索尔碎屑岩岩石学特征及其成因

索尔碎屑岩出露于西藏中部索尔—戈昂错一带,角度不整合覆盖于果芒错蛇绿混杂岩中的地幔橄榄岩之上,粗碎屑岩层和细碎屑岩层互层产出,并见有角砾状灰岩夹层。索尔碎屑岩中粗碎屑岩主要由灰黑色碎屑和土黄色基质所组成;细碎屑岩呈灰黑色,块状构造。碎屑的主体成分为蛇纹岩,并含有少量的尖晶石和斜长石,基质为泥晶结构碳酸盐。碎屑主要呈棱角状—次圆状,边界平直,可能是构造破碎后快速堆积而形成的。在蛇纹岩碎屑边部普遍可见垂直边界生长的板状或粒状方解石,部分碎屑之中方解石呈逐步向内部生长的趋势,而在少量的岩石中已形成了交代残余结构,反映索尔碎屑岩中的碎屑受到了碳酸盐不同程度的交代作用。通过与Gebel Mohagara蛇绿质碳酸盐岩和West Magnitogorsk古岛弧中出露的蛇绿质碳酸盐岩对比研究,初步认为索尔碎屑岩是地幔橄榄岩发生破碎后受到碳酸盐热液流体的交代所形成的。     

Petrology and provenance of late silurian fluviatile sandstones from the ringerike group of Norway

The Ringerike Group, a late Silurian fluviatile sequence in the Oslo Graben of Norway was deposited in two distinct sedimentary provinces. In the northern part of the area the Sundvollen Formation (meandering-stream sediments) and the overlying Stubdal Formation (braided) contain antiperthitic feldspars and drop perthites characteristics of the jotunites of the Jotunheim area of central Norway. Other textural, mineralogical and palaeocurrent evidence supports the conclusion that these two formations were derived from a relatively distant source area, which included the Jotunheim, part of the newly raised Caledonian orogen.To the south, the sandstones of the Holmestrand area are much coarser grained and show a distinctive mineralogy, composition and texture. This evidence, supported by palaeocurrent studies, is consistent with a proximal source area on the eastern flank of the Oslo Graben. Source rocks consisted predominantly of high-grade metamorphic and igneous rocks of the Precambrian basement and the overlying Eocambrian sedimentary rocks.     

尼日尔Termit盆地上白垩统储层岩石学特征及控制因素分析

本文对尼日尔Termit盆地17口井218个井壁取芯样品开展普通薄片、阴极发光、X衍射、扫描电镜及重矿物分析,研究上白垩统储层的岩石学特征,并探讨其控制因素。实验分析结果表明,Termit盆地上白垩统储层的岩石类型主要为石英砂岩,成分成熟度高,以石英为主,含量达86%以上,钾长石、方解石及斜长石等含少量,占比约5%,这种岩石类型对原生孔隙的保存比较有利;填隙物主要为粘土杂基,含量为7%左右,矿物成分以高岭石为主,利于对晶间孔的保留;岩石中发育硅质、方解石和铁质等胶结类型,胶结物的含量占比较小,对储层的破坏作用不大;重矿物类型为磁铁矿、赤铁矿、锆石、磷灰石,推测物源区的母岩类型主要为花岗岩;以细粒结构和少量的不等粒结构为主,分选中等-差,磨圆度一般为次棱角-次圆状,磨圆差。与国内石英砂岩沉积于高能的滨浅海环境不同,研究区石英砂岩成分成熟度高,但分选程度和磨圆度较低,一方面反映了物源区母岩富含石英,同时也反映了这种石英砂岩沉积于近源的河流-三角洲环境。影响研究区上白垩统储层物性的主要因素是岩石类型及成岩作用,由于储层的岩石类型为石英砂岩,压实作用对储层的破坏作用较一般岩石类型偏小。砂岩埋深小于2500m时,主要发育原生孔隙,面孔率大于15%。溶蚀作用对本区储层产生一定的影响,最常见的为长石的溶蚀,溶蚀作用形成粒内溶孔和粒间溶孔,还会扩大原生孔隙形成混合孔,改善了砂岩的储集性能。     

Kaolinite clayrocks in the Triassic Banks Wall sandstone of the western blue mountains,New South Wales

Fine‐grained and coarsely oolitic kaolinite clayrocks that closely resemble in composition, texture, and structure those of the Garie Formation in the southern part of the Sydney Basin are described from the Western Blue Mountains of New South Wales. The kaolinite clayrocks form part of a fine‐grained unit, here designated the Docker Head Claystone Member. It is concluded that the kaolinite clayrocks are the equivalent of the Garie Formation and represent fluviatile accumulations of detritus derived from the same highly weathered source rocks that gave rise to the Garie Formation.     

山西襄汾奥陶系岩石学特征及沉积环境分析

山西襄汾地区奥陶系只有下、中统,主要由碳酸盐岩与蒸发岩组成.燧石及陆源碎屑岩少见。同位素资料表明δ13O较低（平均-5.832‰PDB）,δ13C（平均-1.210‰PDB）变化较小,表示古盐度的指数Z多大于120。微量元素表明碳酸盐岩沉积于近陆环境,受大气淡水影响强烈。沉积环境主要是潮上（膏泻湖）、潮间坪、潮下局限海及开阔海。峰峰期后最大的海退结束了本区海相沉积史。     

淄博市淄川区饮用天然矿泉水赋存条件与形成机理研究

淄博市淄川区饮用天然矿泉水按照含水层性质可划分为松散岩类孔隙水、碳酸盐岩类裂隙岩溶水和岩浆岩类构造裂隙水3大类。区内29眼井泉监测点饮用天然矿泉水检测结果显示,研究区存在锶型、锂型和锶锂复合型3种类型矿泉水。从水岩作用角度分析了矿泉水中锶和锂的来源,认为研究区广泛分布寒武纪碳酸盐岩,石灰岩尤其是鲕状灰岩中丰富的锶元素,是锶矿泉水形成主要的物源条件之一;地下水沿灰岩裂隙岩溶运动为矿泉水的形成创造了重要的水动力条件;研究区腐殖质经低矿化近中性的大气降水淋滤后,形成富含腐殖酸的偏酸性溶液入渗地下,对地下岩层产生溶解、溶滤作用,随着溶解过程的进行,岩石中的锶元素大量进入地下水中。     

包含变质岩分类三要素的主要变质岩分类表

变质岩分类的三要素是:变质岩的物质成分(化学成分、矿物成分)、变质岩的组构(结构、构造)和变质岩的成因(变质作用类型和形成变质岩的物理化学条件).由于变质岩的化学成分、矿物成分、组构特征和形成变质岩的地质环境十分复杂,致使至今尚无以变质岩分类三要素为基础的、内容比较完善的分类方案.本文中主要变质岩的分类是以其分类三要素为基础编制的,首次将不同成因的变质岩类并列于同一表中、将鉴定变质岩的主要标志性矿物成分和组构特征列入同一分类表中.该分类对鉴定变质岩石具有可操作性和实用性,分类表中涵盖了自然界主要的变质岩石.     

Mineral chemistry and petrogenesis of granular ejecta from the Alban Hills volcano (Central Italy)

Summary A suite of lithics (ejecta) collected from the latest erupted pyroclastic products of the Alban Hills volcano (Central Italy) has been studied to determine their mineralogical composition and to investigate their genesis. The ejecta commonly have granular texture and consist of coarse-grained crystals often associated with a fine- to medium-grained matrix. The mineralogical composition is variable and consists of both typical igneous minerals and contact metamorphic phases. Garnet, clinopyroxene K-feldspar are almost ubiquitous, whereas leucite, wollastonite, sodalite-group minerals, phlogopite, nepheline and phillipsite are present in most of the ejecta; minor and accessory phases include cuspidine, amphibole, pyrrhotite, magnetite, apatite, uranpyrochlore, sphene, kalsilite, and melilite; anorthite, zircon and fluorine-bearing Ca, Zr silicate phases, larnite, and baryte are found sporadically. Ca, REE, Th silicophosphates occur in many samples generally disseminated along interstices and fractures of main minerals. Calcite is present as discrete crystals sometimes enclosed in other minerals, as granules in the fine-grained matrix and as late microcrystalline veins. It shows high oxygen and low carbon isotope ratios with δ¹⁸O = + 17.96 to + 27.19, and δ¹³C = −4.74 to −19.57. Clinopyroxene ranges from diopside to compositions strongly enriched with both Ca-Tschermak’s and esseneite components. Feldspars are generally potassic even though Ba and Sr are found in significant concentrations in some samples. K-feldspars from wollastonite-bearing ejecta are often rimmed with elongated felty crystals identified by X-ray diffraction analysis as leucite. These feldspars show a depletion in Si, and enrichment in Al and K from core to rim. Significant compositional variations are also shown by various other phases such as nepheline, apatite, Ca, REE, Th silicophosphate. The occurrence of igneous and contact metamorphic minerals, as well as the chemical variations of clinopyroxenes and feldspars in the investigated ejecta reveal complex genetic processes related to the interaction between potassic magma and wall rocks. The Ca-rich composition of most phases points to a carbonate nature for the wall rocks. Textural evidence suggests that coarse-grained rocks formed at the margin of the magma chamber were invaded by a late, volatile rich potassic liquid which crystallized as a fine-grained matrix and produced disaggregation and reaction of early formed minerals. Fluid phases percolating through the rocks generated infiltration metasomatism and deposited some uncommon phases rich in Ca, REE, Th, U, which are found along cracks and at the margins of early crystallized minerals. Overall, the all spectrum of the minerals found in this study are also typical of carbonatitic rocks. Their presence in the Alban Hills ejecta demonstrates that their genesis can be related to interaction between ultrapotassic melts and carbonate wall rocks, in addition to precipitation from carbonatitic melts. Received February 20, 2001; revised version accepted September 23, 2001     

Chemical modification of enclave magma by post-emplacement crystal fractionation,diffusion and metasomatism

Hornblende-bearing microgranitoid enclaves from the Swifts Creek Pluton (SCP), SE-Australia display mineralogical and textural variations from their margins to their centers. Margins are fine grained and display quench textures and are enriched in amphibole, biotite and in some cases magnetite relative to their coarser grained centers. Enclaves of this type and their adjacent granitoid host rocks have been sectioned into 0.3 to 1 cm thick slabs in order to determine the chemical variations associated with these mineralogical changes. The fine grained margins are variably enriched in Ti, Al, Mg, Fe, Mg, K, Rb, Ba, Nb, Y, Sc, V, Ni and the REE up to a factor of three relative to the enclave centers. This enrichment is compensated by a depletion of Si and Zr. Elements like Ca, Na and Sr show less coherent variation from margin to center. Host rocks in immediate contact with these enclaves are depleted in Mg, Na, K, Rb and Ba relative to host rocks that are not exposed to enclaves. No one single process can account for all the variations. Instead, we propose that the chemical variations are related to a combination of in situ crystal fractionation of isolated magma globules, mass transfer by diffusion and metasomatic exchange.     

发育完整的灰岩风化壳及其矿物学和地球化学特征

对于碳酸盐岩土覆土壤成因、尽管碳酸盐岩风化残积成土说被多数学者认同,但由于碳酸盐岩中酸不溶物含量极低,在风化成土过程中会伴随着巨大的体积缩小变化,原岩结构和半风化带无法保留,从而缺失了探索上覆土壤物质来源的重要中间环节,使得这种观点缺乏野外宏观证据的支持。最近,我们在贵州、湖南等地发现了数个以泥质灰岩和泥质白云岩为基岩的碳酸盐岩风化壳剖面,尚保留有较好的原岩结构,具有明显的风化壳分带和过渡现象。这些风化壳剖面的发现为深入研究碳酸盐岩风化成土过程提供了良好的研究场所。本文选取了较为典型的吉首泥灰岩风化壳剖面,从矿物学地球化学的角度来探讨碳酸盐岩风化壳的形成过程和发育特征,结果表明该风化壳既遵循非碳酸盐岩（主要是结晶岩类）风化壳的发育特征,也具有自己独特的地球化学演化规律。风化壳总体特点受碳酸盐中的酸不溶物矿物组合及化学成分的影响甚至控制,风化非碳酸盐风壳相似的发育特征。吉首泥灰岩风化壳剖面的发育特征和作者早先提出 的碳酸盐岩风化成土的两阶段模式是一致的,即以碳酸盐矿物大量淋失、酸不溶物逐渐堆积或残积为特征的早期阶段和残积物进一步风化成土的阶段,后一阶段的演化类似非碳酸盐岩类的风化过程。     

Comparison of neutron and X-ray diffraction in texture analysis of deformed carbonate rocks

The paper compares pole figure determinations with neutron diffraction and X-ray diffraction on experimentally deformed carbonate rocks, a coarse grained marble and fine grained limestone. Neutron diffraction enables determination of complete pole figures on a single spherical specimen and is advantageous for coarse grained materials. Results obtained with both diffraction techniques agree satisfactorily, although uncertainties introduced by counting statistics are more serious for neutrons than for X-rays. Continuous detectors add new possibilities which are still little explored.     

中国软玉矿床类型及其矿物学特征

文章将中国11个产地的软玉（透闪石玉）矿床分为岩浆热液型和变质热液型两大类。其中岩浆热液型又根据侵入体的性质分为中酸性岩型、基性岩型、超基性岩型;变质热液型根据母岩特点分为碳酸盐岩型和蛇纹岩型,并从围岩和侵入岩体特征、矿体产状及大地构造背景等方面,对比分析了软玉矿床的相似性和差异性,总结了各产地软玉的品种、矿物成分、结构构造等矿物学特征;简单分析了软玉的找矿远景。