Sedimentary Circumstances and Physiographic Sites Impact on the Morphological Properties of Feldspar Minerals of Iraqi Soils

The current research aimed to investigate the effect of sedimentary conditions, physiographic locations, proximity, and distance from the source on the morphological characteristics of feldspar minerals diagnosed by Scanning Electron Microscope (SEM) for some selected soils from northern and southern Iraq. The results of SEM present the emergence of a series of surface changes, corrosion, and the absence of healthy surfaces on the surfaces of orthoclase metal. It is dominated by roundness or sphericity, with the polishing of the metal surfaces coinciding with the phenomenon of roundness and sphericity. The edges of the orthoclase mineral were less affected due to being transported over long distances with transported river deposits. The presence of long lines indicates that the metal is subject to weathering and change. One of the most critical manifestations of change occurring on the surfaces of feldspars is the emergence of long parallel lines, which are called linear parallels, which reflect the severity of weathering to which the feldspar minerals were subjected. The morphological characteristics of the surfaces of the mineral microcline appeared under the SEM similar to those shown by the surfaces of the mineral orthoclase with clarity of the phenomenon of linear parallelism and a decrease in the phenomena of sphericity and polishing compared to the surfaces of the mineral orthoclase, which is less stable and resistant to weathering than the microcline. There was a phenomenon of accumulated plates on the surface of the metal, with the edges of the metal being subjected to weathering processes with greater intensity than the surface areas, despite the expansion of the surface area of the metal particles. The appearance of plagioclase of albite type and the edges of its particles were less affected by the weathering processes compared to its surfaces. The reason is attributed to the fact that the edges area is more susceptible to erosion and grinding during transport. This discrepancy in the morphological characteristics of feldspar minerals is attributed to their influence on the processes of weathering, transport, and sedimentation in the soils of the study areas and to the variation in their physiographic locations and their distance and proximity to the Iraqi-Iranian border strip in southern Iraq within the sedimentary plain affected by sediments coming from the heights of Iran in addition to being affected by the sediments of the Tigris River.


Introduction
Feldspar minerals belong to the group of Tectosilicate minerals.They are one of the most abundant minerals in the Earth's crust, making up about 50-60%.Therefore, they are of great importance in identifying the geology and material of the origin of the soil and the factors of soil formation.They are also important in the inheritance and development of the soil due to their location in the middle of the formative interactive series of primary minerals with time [1].Feldspar minerals are rock-forming silicate minerals containing sodium, calcium, potassium, and barium [2].Among the most common aggregates are the plagioclase feldspar group, including sodium and calcium, and the primary feldspar group, including potassium and Sodium [3].There are four chemical groups of feldspar: potassium feldspar KAlSi 3 O 3 , sodium feldspar NaAlSi 3 O 3 , calcium feldspar CaAlSi 3 O 8 , and barium feldspar BaAlSi 3 O 3 [4,5] .Feldspar minerals are present in very coarse parts, at a rate of 12%, in the coarse parts of the sand 0.5-2.0mm [6].[7] Feldspars have the general chemical formula MT 4 O 8 , substituting 25% silicon and 50% aluminum in the T sites occupied by ions such as Na + , K + , Rb + , Ca +2 , Sr +2, or Ba +2 [8].Aluminum and silicon are distributed randomly.The average site occupancy for each tetrahedron is 25% aluminum and 50% silicon, so the basic structure consists of a ring consisting of four tetrahedral shapes with alternating pairs of vertices pointing in opposite directions.Feldspars' crystal structure breakdown at lower temperatures is around the interstitial cation.The larger cations, such as potassium or barium, resist collapse, making them maintain their elongated structure.However, smaller cations such as sodium and calcium cannot resist collapse, which leads to distortion in the structure or crystal structure, thus reducing the symmetry to triclinic.At lower temperatures, Si and Al tetrahedral tend to arrange the structure.It is a prolonged process compared to structural distortion, breaking strong Al-O and Si-O bonds.The structural distortion is strongly dependent on silicon and aluminum ions.Feldspar minerals are distinguished by their monoclinic and triclinic crystals.Under low temperatures, a semi-stable two-component solid solution includes orthoclase and albite.Under conditions of low cooling, that is, when the temperature of the solution decreases slowly, an increase in its components occurs, which leads to a process of overlapping growth between these components so that semi-parallel and alternating flakes of sodium and potassium are formed, which eventually lead to the appearance of the mineral perthite and antiparasite.The plagioclase in Alberthite existed in the form of films and veins or patches arranged in the orthoclase and microcline.The reverse perthite is the opposite of the normal perthite, i.e., the orthoclase is arranged in twin levels of the plagioclase.Perthite is formed due to the immiscibility of solutions, exsolution, or as a result of replacement processes or metasomatism between potassium feldspar and sodium-rich solutions [8]. 3 Weathering feldspar leads to the complete fragmentation of the crystalline lattice and the formation of aluminum wires, hydroxides of silicon, iron, and aluminum, as well as oxides of potassium, sodium, and calcium, finally forming clay minerals [9].The resistance of feldspar to weathering decreases with the increase in temperature, so the difference is attributed to the degree of crystallization at different temperatures.The purity of the mineral, the size of the mineral, and the surrounding environmental conditions all affect the speed of the weathering process.The weathering process is one of the most common processes to which feldspar minerals are exposed.It transports and depo sits clays and iron oxides on the surfaces of feldspar minerals [10].The K 2 O/Na 2 O ratio is essential in restoring the dominance of different feldspar minerals [11].This ratio refers to the conditions of chemical weathering, which lead to the transfer of the relatively small and fast-moving sodium element while maintaining the more significant and slower-moving potassium concentration.Therefore, in the conditions of chemical weathering, the dominance of potassium feldspar minerals is more than that of calcareous feldspar.Feldspar minerals show chemical resistance to environmental changes such as temperature, humidity, and fluid formation.Potassium feldspar is more resistant to changes than plagioclase feldspar [12].Sand minerals as one of the natural resources scattered in the Earth's crust, which are products of the weathering processes of the various source rocks.Feldspar minerals are one of the essential components of sand minerals, and it is of great importance in the study, inheritance, and development of soils.Due to the lack of available studies on feldspar minerals, especially in Iraqi soils, and due to the multiplicity of its sources, which included sediments of the Tigris and Euphrates rivers and torrents coming from the mountainous heights at the Iraqi-Iranian border strip, this current study aimed to study the effect of distance or proximity to the sources of sedimentation on the morphological properties of these minerals.

Field Procedures
Sites from southern Iraq, including the governorates of Wasit and Maysan, and northern Iraq, including Erbil and Sulaymaniyah, were selected for this study.Three sites were selected from Wasit Governorate: Badra, Zurbatiya, and Zubaydiyah, two from Maysan Governorate, Ali Al-Gharbi, and Al-Tayyib, three from Erbil Governorate that are Juman, Soran, and Shaqlawa, and two from Sulaymaniyah Governorate that is Sayed Sadiq and Dukan for this study.The samples were taken at two depths, surface (0-30) cm and subsurface (30-60) cm.

Preparation of Samples for Mineral Analyzes
Soil samples were collected from the specified sites, transferred to the laboratory, and air-dried.First, the samples were manually hammered with a polyethylene hammer to preserve the morphology of the minerals.Then, they were passed through a sieve with a diameter of 2 mm.The samples were kept in plastic boxes, numbered, and ready for mineral analysis.Next, the sand was separated by the wet sieving method, using a sieve with a diameter of 50 micrometers from the separating silt and clay.

Examination of Sand Samples by Scanning Electron Microscope (SEM)
Selected samples of sand separators were examined for some soils under study and surface and subsurface depths after air drying and powdering.Afterward, they were scattered on unique platforms of the scanning electron microscope of the type (inspect F50 FE-SEM) to study the morphological characteristics of feldspar minerals in the sand separator.

Physical Properties of Feldspar Minerals
The morphological properties of feldspar minerals, which SEM identified, were studied for some selected samples from the soils of some regions under study.In addition, the light part within the sand separation was examined based on the presence of feldspar minerals within the light part of the sand particles.

Orthoclase Mineral
The results of electron microscope examinations, Figure 2, within the soils of Ali Al-Gharbi, Al-Tayyib, Badra, and Juman regions present that roundness or sphericity dominates the morphological characteristics of the mineral Orthocles.In a previous study, it was found that the shape of the mineral particle is defined by the amount of its roundness or its closeness to the spherical shape, while the sharpness of the curvature of the corners and edges of the particle defines the roundness [13].The phenomenon of polishing the surfaces of the metal, Figure 2, in the soil of Badra and Juman, coincides with the phenomenon of sphericality or roundness.This state of polishing may be attributed to several reasons, including the deposition of materials that may be vitreous or scalloped, shiny on the surfaces of feldspars, or to the activity of microorganisms that enhance some compounds on the surfaces of these minerals, which work to smooth the bumps on their surfaces, turning them into smooth surfaces.Moreover, it has been subjected to regular mechanical corrosion due to continuous rolling during the water transport operations and for long distances, assisted by the weak state of crystallization of the mineral particle compared to other mineral particles.This phenomenon is prevalent in tiny particles of coarse sand separators [8].The edges of the orthoclase mineral appeared less affected under the SEM, which is attributed to being transported over long distances with transported river sediments.The results also present the absence of cracking on the surfaces of orthoclase minerals, which is attributed to the high resistance of the mineral to various weathering processes [14].However, the results of the scanning electron microscope, Figure 2, in the soil of Zubaydiyah, Al-Tayyib, and Badra of the surfaces of the orthoclase mineral showed the presence of long lines, which indicates the exposure of the mineral to weathering and change.One of the most important manifestations of the change occurring on the surfaces of feldspars is the emergence of long parallel lines, which are called linear parallels, which reflect the severity of weathering to which the feldspar minerals were subjected [15].The results of the microscopic examinations, Figure 2, of Ali Al-Gharbi, Al-Tayyib, and Soran soils present that the edges of the orthoclase mineral appeared eroded, scratched, and with imperfect faces.The reason is attributed to the transformation of the orthoclase mineral to other minerals, such as sericite or kaolinite, by the influence of various weathering factors, especially chemical ones, or they are transformed into minerals with more stability [16].However, they mentioned in a previous study that the intact edges of the orthoclase minerals indicate that they are newly formed and produced from the source and are not exposed to severe weathering during the transportation and sedimentation processes [17].

Microcline
SEM examination presents the morphological characteristics of the surfaces of the mineral microcline, Figure 3, in the soils of Shaqlawa, Badra, and Soran.It appeared similar to those shown by the surfaces of the mineral orthoclase with clarity of the phenomenon of linear parallelism and a decrease in the phenomena of balling and polishing compared to the surfaces of the mineral orthoclase, less stable and resistant to weathering than the mineral microcline.In a previous study of the edges and surfaces of the microcline mineral, it was found that Bidoun Jassan soils were subjected to weathering processes but with less intensity compared to the plagioclase mineral particles in Bidoun Alkhalil soils [15] .In this study, the surface of the mineral appeared in a zigzag pattern, not cracked, and the reason for this is due to the nature of the resistance of the two minerals to the different weathering processes.Microcline is more resistant to weathering than plagioclase.The nature of the chemical composition and texture of the parent material forming the rocks and the difference in the degree of crystallinity affected by the temperature of different minerals affect the degree of their susceptibility to different weathering processes [18].The phenomenon of accumulated plates on the surface of the mineral, Figure 3, in the soils of Shaqlawa and Juman, with the edges of the mineral subjected to weathering processes more intensely than the surface areas despite the expansion of the surface area per minute of the mineral.The reason was attributed to the vulnerability of areas of weakness in parts of the mineral to weathering processes more than the rest of the parts of the mineral [19].

Plagioclase
Electron microscopy examinations present the appearance of albite-type plagioclase, Figure 3, of the soils of Dukan and Sayed Sadeq.However, the edges of its particles were less affected by the weathering processes than its surfaces.The reason is attributed to the fact that the edges area is more susceptible to erosion and grinding operations during transport operations.Therefore, the edges of the water-borne mineral particles are more affected by transport and sedimentation processes than the surface area, as confirmed by [20].On the other hand, the surfaces of the plagioclase mineral, Figure 4, of the soils of Sayed Sadiq and Dukan were affected by the weathering processes that took place at the source areas (affected by the sedimentation of the border strip and the sedimentation of the Tigris River) in succession, due to the short distance traveled by those particles during transportation and their deposition in their current locations, especially chemical weathering.In general, the results of electron microscope examinations of the surfaces of the orthoclase minerals of the soil under study showed the emergence of a series of changes that indicate physical changes that occurred on them.One of its most essential manifestations is the scarcity of intact surfaces unaffected by the various weathering processes.Traces of cracking and fragmentation appeared on their surfaces due to transport and sedimentation processes.The results present that the morphological properties of the surfaces of potassium feldspar (microcline) and plagioclase (albite) were similar to those shown by the surfaces of potassium feldspar (orthoclase).However, the surface of the albite mineral appeared to be more subject to mechanical fracture with the presence of the phenomenon of linear parallelism and the decrease in the phenomena of balling and polishing, compared to the surfaces of the mineral orthoclase, which is less stable and resistant to weathering than the mineral microcline.Potassium feldspar minerals, microcline, are more resistant to weathering than plagioclase feldspar.The difference between orthoclase and microcline in the shape of the crystalline structure led to a difference in the degree of their resistance to weathering.Therefore, the orthoclase mineral, which has a monoclinic crystalline system and has an irregular arrangement of silicon and aluminum ions within its crystalline structure, is less resistant to mechanical shattering during the transport and sedimentation process compared to the mineral microcline crystallized within the triclinic system, which has a regular arrangement of silicon and aluminum ions within its crystalline structure.This discrepancy in the influence of feldspar minerals on the processes of weathering, transport, and sedimentation in the soils of the study areas is attributed to the variation in their physiographic locations and their remoteness and proximity to the Iraqi-Iranian border strip in southern Iraq within the sedimentary plain affected by sediments coming from the heights of Iran in addition to its influence by the sedimentation of the Tigris River.It is consistent with a study by [9].The soils of the Ali Al-Gharbi area are considered a border area within the governorate of Missan, affected by the sediments of Iran [20] .The regions of northern Iraq are considered border areas between Iran and Turkey, and their soils are affected by sediments coming from the highlands of Turkey and Iran, in addition to being affected by river sediments, which was confirmed by [21].Joman region is considered one of the areas affected by the border strip due to its proximity.The Tigris River's sediments affect Soran and Sayed Sadeq regions' soils.Accordingly, this difference is in the physiographic sites, transport processes, sedimentation conditions, the extent of their proximity and distance from the source of sedimentation, and the various weathering processes, especially chemical weathering, and the accompanying transformations and changes of those minerals.The presence of potassium feldspar indicates the presence of simple chemical weathering, close transport distance, and sedimentation velocity [22].

Conclusions
Two types of potassium feldspar, including mineral (orthoclase and microcline) and plagioclase (albite), were identified under a scanning electron microscope.The morphological characteristics of the surfaces of potassium feldspar (microcline) and plagioclase (albite) were similar to those shown by the surfaces of potassium feldspar (orthoclase).However, the surface of the albite mineral appeared to be more subject to mechanical fracture with the presence of the phenomenon of linear parallelism and the decrease in the phenomena of balling and polishing, compared to the surfaces of the mineral orthoclase, which is less stable and resistant to weathering than the mineral microcline.The potassium feldspar minerals microcline is more weathering-resistant than the plagioclase feldspar.In addition, the difference between the minerals orthoclase and microcline in the shape of the crystal structure led to a difference in the degree of their resistance to weathering.These differences in the morphological characteristics of the identified feldspar minerals reflect the influence of the physiographic sites, transport processes, sedimentation conditions, the extent of their proximity and distance from the source of sedimentation, the various weathering processes, especially the chemical weathering on their edges, their surface characteristics, and the accompanying mineral transformations and changes to other minerals.

Figure 1 .
Figure 1.Diagram of the formational phase of the stages of formation of various feldspars at high and low temperatures.

Figure 2 .
Figure 2. SEM examinations of the orthoclase mineral in the tested soils.

Figure 3 .
Figure 3. SEM examinations of the mineral microcline in the studied soil.

Figure 4 .
Figure 4. SEM examinations of the mineral plagioclase in the soils under study.