Ancient Egyptian Granite Graffiti of Bigeh Island, Philae Archaeological Site (Aswan, Egypt): An Archaeometric and Decay Assessment for Their Conservation

Abstract

This study investigates the deterioration of granite graffiti at the Philae Archaeological Site on Bigeh Island (Aswan, Egypt), attributed to Khaemwaset (1281–1225 BCE, 19th Dynasty). These graffiti, despite being carved into durable Aswan granite, are experiencing progressive degradation due to environmental and hydrological factors. This research aims to analyze the mineralogical and chemical transformations affecting the graffiti to provide a comparative assessment of submerged and unsubmerged granite surfaces. A multi-analytical approach was employed, combining petrographical examination, X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) to identify compositional changes and deterioration patterns. The results indicate mineralogical transformations in submerged and periodically exposed surfaces. The granite primarily consists of quartz, feldspar, and biotite, with notable alterations including kaolinization and illitization and dissolution of feldspar minerals and biotite oxidation. These processes are directly linked to prolonged exposure to fluctuating water levels and recurrent wet–dry cycles, which accelerate granular disintegration, exfoliation, and surface loss. Additionally, salt crystallization, particularly halite, contributes to granite weathering, while sulfate interactions promote chemical weathering. In addition, biofilm colonization, facilitated by high moisture retention, further exacerbates surface deterioration by producing organic acids that weaken the mineral matrix. Finally, the results confirm the need for conservation interventions to mitigate ongoing damage.

1. Introduction

Granite is a widely studied igneous rock due to its durability and resistance to weathering; its inherent properties make it a valuable natural stone for construction. Several researchers have examined the relationship between granite’s mineralogical composition and environmental factors. Their studies provide information about its behavior under various conditions, including prolonged exposure to water [1,2,3,4]. One of the primary processes affecting granite is chemical weathering, primarily influenced by the presence of water and atmospheric CO₂. According to White and Brantley [5], feldspar, a dominant mineral in granite, undergoes hydrolysis, transforming into clay minerals like kaolinite while releasing dissolved ions such as potassium, calcium, or sodium into the environment. This reaction is accelerated under acidic conditions, highlighting the role of environmental pH in granite weathering. The study emphasized that quartz, due to its resistance, often remains as a residual component in weathered granite. Moreover, granite’s interaction with severe water conditions, such as those in marine or highly saline environments, has also been a subject of interest. In this sense, Chabas and Jeannette [6] explored the role of salt weathering in degrading granite structures, particularly in coastal areas. Salt crystallization within granite’s microcracks can lead to significant stress, resulting in granular disintegration and surface exfoliation. Other works have investigated the impact of freeze–thaw cycles on granite in cold climates [7,8,9,10]. These studies emphasized that the repeated freezing and thawing of water within the pore spaces of granite leads to mechanical weathering, with microcracks forming and propagating over time. This process, though slower than chemical weathering, can significantly reduce granite’s structural fabric in the long term. In the context of severe water conditions, the solubility and leaching of minerals from granite have been studied in laboratory simulations [11,12]. Farquharson et al. [13] demonstrated that granite subjected to high-flow water systems, particularly those containing acidic or highly mineralized water, showed increased leaching of potassium, calcium, and other ions affecting the porosity, permeability, and Young’s modulus ranges. This phenomenon was particularly evident in granites with higher feldspar content, indicating a direct relationship between mineral composition and susceptibility to water-induced alterations. Additionally, its resistance to water also depends on its porosity and microstructural features. Winkler [14] noted that granites with low porosity (<1%) and fine-grained textures are less affected by water penetration and related deterioration. However, when granites with larger grain sizes and more interconnected pores are exposed to water, the risk of structural decay increases significantly. The role of biological factors in granite weathering under environmental conditions has also been studied. Gadd [15] reviewed the contribution of microbial activity to granite alteration. Lichens and fungi secrete organic acids that enhance the dissolution of feldspar and biotite, promoting the breakdown of granite surfaces. Such biodeterioration is often observed in monuments and buildings constructed with granite in humid environments.

The granite of Aswan is a notable natural stone widely used in ancient Egyptian architecture and is characterized by its unique mineral composition and geological properties [16,17,18]. This granite is primarily composed of quartz, feldspar (both orthoclase and plagioclase), and biotite mica. Quartz, accounting for approximately 20–30% of the composition, contributes to the stone’s durability and resistance to weathering [19,20]. Feldspar, often orthoclase, represents the predominant mineral at around 60%, imparting the characteristic pink to reddish hue due to the presence of potassium (K). Plagioclase feldspar adds to the granite’s overall textural variety, while biotite mica (5–10%) provides a dark contrast within the stone, enhancing its aesthetic appeal [21]. The granite also contains trace amounts of accessory minerals such as zircon, apatite, and magnetite, which contribute to its unique coloration and density. Zircon is particularly valuable in geochronological studies, aiding in determining the stone’s formation age [22]. The granitic rock’s high density and compressive strength, approximately 200 MPa, make it suitable for monumental structures. Additionally, its low porosity (<1%) ensures minimal water absorption, an essential property for the longevity of ancient architectural works [23]. Hence, the mineralogical and chemical attributes of Aswan granite not only defined its durability but also influenced its historical significance, as seen in its extensive use in constructing obelisks, statues, and temple elements in ancient Egypt.

The current research focuses on the mineralogical composition and conservation challenges of one of the most significant granite graffiti inscriptions on Bigeh Island, dating back to approximately 1281–1225 BCE and located at coordinates 24°00′55″ N, 32°52’55″ E (Figure 1A). In this area, there is no comprehensive condition assessment for graffiti stelae in Bigeh for conservation purposes. These graffiti commemorate the first three Sed-Festivals of Pharaoh Ramesses II, which were important royal renewal rituals. They were carved under the supervision of Prince Khaemwaset, a son of Ramesses II known for his efforts in monument restoration, and indicate that the first Sed-Festival was proclaimed and celebrated in the 30th regnal year, the second was proclaimed in year 33 and held in year 34, and the third was celebrated in year 37, though details remain limited. Additionally, the names of later rulers such as Psamtik II (595–589 BCE) and Ahmose II (570–526 BCE) were also recorded, signifying the continued importance of Bigeh Island in different periods. Historically, graffiti of this kind were often inscribed by priests, military expeditions, or commercial travelers, as Bigeh Island, known in ancient times as Abaton, held religious significance, particularly in relation to the cult of Osiris [24]. The Temple of Bigeh and the surrounding rocky surfaces, as observed by Blackman in [25], contain numerous inscriptions, emphasizing the site’s ritualistic and commemorative function. However, despite their historical value, these granite graffiti and surrounding monuments face significant conservation challenges due to natural erosion, weathering, and human-induced damage, necessitating urgent documentation and preservation efforts [26].

On Bigeh Island, there is a research gap in comprehensively assessing the granite graffiti stelae in various local environmental conditions (unsubmerged and submerged states) for conservation purposes. Consequently, this work aims to highlight the durability and conservation challenges of the granite that bears significant graffiti, emphasizing the importance of its preservation and considering the different conditions between unsubmerged and submerged granite within the Nile River and surrounding environment. To achieve this, the following work was conducted:

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Extensive site observation was conducted for documentation and visual assessment, and a multi-analytical approach was employed to analyze material composition and deterioration mechanisms.

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X-ray diffraction (XRD) and X-ray fluorescence (XRF) were used for mineralogical and chemical analysis and analysis of the potential alteration of by-products due to water exposure and reaction.

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Petrographic description of the rock texture, grain boundaries, and mineral relationships was used to assess weathering patterns. Additionally, microscopic analyses were carried out using digital microscopy to study surface morphology and detect microfractures, and scanning electron microscopy (SEM) with EDS was used to analyze the surface morphology and the elemental compositions at high resolution to provide a comprehensive understanding of decay processes.

Finally, the results support the development of effective conservation strategies for safeguarding the graffiti, and the environmental and hydrological conditions were considered in assessing stone stability and surface decay.

2. Materials and Methods

This study was conducted at Bigeh Island, Philae Archaeological Site (Aswan, Egypt), where ancient Egyptian granite graffiti were analyzed to determine their mineralogical composition and decay mechanisms. They are located near the Nile River (Figure 1B), exposing them to environmental factors such as wind, water-induced weathering, biological activity, and salt crystallization. Granite samples were collected from both submerged and unsubmerged areas of the site. The submerged samples were taken from rock surfaces partially or fully exposed to the Nile’s water (red star, Figure 1B), while the unsubmerged samples were retrieved from dry areas of the site (yellow star, Figure 1B). A total of 4 highly weathered fragments of granite samples were collected (2 from unsubmerged areas and 2 from submerged areas), with dimensions of around 5 cm × 5 cm × 3 cm for each. Some samples were used as fragments for thin section and microscopical analysis and some pieces were prepared in a powdered state for mineralogical and chemical analysis.

A comprehensive in situ visual assessment was conducted to document the physical state of the granite surfaces. Decay phenomena such as cracks, exfoliation, granular disintegration, and biological colonization were mapped and recorded. High-resolution digital imaging and decay mapping techniques were employed to capture the extent of deterioration.

For the hand sample description, a digital microscope (USB binocular microscope with stand) (Manufactured by Celestron in Torrance, USA) with magnification between 20 and 400× and equipped with a digital camera of 1.3 Mpx was employed to assess the surface texture and morphological changes in unsubmerged and submerged granite samples. Digital microscopy was primarily used for initial surface observations. The microscopic observations focused on surface roughness, mineral grain detachment, biological colonization, and encrustation. The presence of microcracks and alteration halos surrounding feldspar and biotite minerals was documented.

Thin sections of both unsubmerged and submerged samples were prepared and examined under a polarized optical microscope (POM) (Leica DM2700 P, manufactured by Leica Microsystems in Wetzlar, Germany). This analysis identified mineralogy and textures, and alteration features and decay patterns. Additionally, and for higher-resolution finer-scale microstructural analysis, a scanning electron microscope (SEM, Nova NanoSEM 450), with a voltage between 200 V and 30 kV, resolution of 3.0 nm at 30 kV and 10 nm at 3 kV, and supplied with an EDAX 60 mm 2 Octane Super EDS detector (Manufactured by FEI Company in Hillsboro, OR, USA), was used to examine the microstructural characteristics and surface morphology of the granite samples. The EDS analysis provided elemental composition data, highlighting weathering-induced changes, salt crystallization, and biological interactions affecting the granite inscriptions. Granite samples from unsubmerged and submerged environments were sectioned into ~1 cm³ pieces. Each sample was mounted on an aluminum stub using carbon tape and sputter-coated with a ~10 nm gold layer to enhance conductivity.

X-ray diffraction (XRD) analysis was conducted to determine the mineralogical composition using a Bruker D8 Advance diffractometer equipped with a high-speed measurement Lynxeye detector, using the following specifications: CuKα radiation filtered by Ni, graphite monochromator, and fixed slots, and 2theta 5° to 60° scanning angle. Diffractograms were interpreted with EVA software (Bruker-AXS) (Manufactured by Bruker AXS in Karlsruhe, Germany). Representative samples from both environments were milled using an agate mortar and ground to a fine powder (<45 µm) to ensure homogeneity. The powder was packed into a sample holder using the back-loading method to achieve random crystallite orientation. Finally, portable X-ray fluorescence equipment (Thermo scientific Niton XL3t Goldd+) (Manufactured by Thermo Fisher Scientific in Tewksbury, MA, USA) was used to identify the elemental composition of two representative granite samples by finely grinding and directly analyzing them using a pressed powder pellet technique to analyze them by XRF.

All analysis was hosted in the Department of Earth Sciences (UGEA-PHAM service) and the Central Services of Scientific and Technological Research (SC-ICYT) at the University of Cadiz (Spain).

3. Results and Discussion

3.1. In Situ Analysis and Granite Decay

The granite rock surfaces carrying ancient Egyptian graffiti near the Nile River exhibit various forms of weathering and decay. The categorization of mechanical, chemical, and biological weathering of the studied graffiti is explained and summarized in

Table 1. The observed decay processes affecting the ancient Egyptian graffiti under mechanical, chemical, and biological weathering.

Decay Type	Observations	Causes and Effects
Mechanical Weathering
Diaclases and cracks	Found in rock formations (Figure 2A,B)	Caused by natural stress and thermal expansion/contraction due to extreme wet–dry variations; widening of fractures compromises structures.
Granular disintegration and surface erosion	Inscriptions show loss of mineral grains (Figure 2C,F)	Wind, moisture, and water flow weaken mineral cohesion, dislodging grains over time; this is increased by salt crystallization.
Flaking and exfoliation	Peeling rock layers (Figure 2E)	Hydration and dehydration cycles due to periodic submersion in Nile water. In addition, salt crystallization causes surface detachment.
Mechanical erosion	Surface degradation from sediment transport (Figure 2F)	Strong water currents and suspended particles cause abrasion, accelerating decay.
Chemical Weathering
Salt crystallization	Internal stress and degradation	Dissolved salts in Nile water enter rock pores, crystallize, and expand, and this causes structural weakness.
Chemical reactions with Nile water	Loss of granite internal fabric	Sulfates and carbonates in water that react with granite minerals can promote decay.
Increased porosity	More porous structure due to repeated wetting and drying cycles	Water infiltration enlarges micropores and increases the susceptibility to further decay.
Black crust formation	Surface discoloration	Accumulation of atmospheric pollutants leads to chemical weathering.
Biological Weathering
Vegetation growth (algae, moss, lichen)	High moisture retention (Figure 2B,D)	Organisms produce organic acids that chemically degrade minerals, increasing erosion.
Bird waste accumulation	Surface damage (Figure 2C)	Organic acids from waste weaken the granite surface, contributing to further deterioration.
Moisture retention by biological growth	Increased salt crystallization	Retained moisture accelerates chemical and mechanical weathering.

. These graffiti are exposed to environmental factors that contribute to their gradual deterioration. A comprehensive condition assessment through in-site visits reveals multiple forms of damage, primarily caused by water exposure, structural instability, biological activity, and salt crystallization. One of the most prominent issues observed is the presence of diaclases (Figure 2A,B). These diaclases are exposed to natural stress, increased by the thermal stress, which contributes to granite expansion and contraction due to extreme temperature variations between day and night. Over time, such stress leads to the widening of natural fractures, which compromises the structural behavior of the rock. Additionally, Peng et al. [27] confirmed that repeated thermal exposure for granite can change the mass, volume, and density of granites, causing intergranular cracks and transgranular cracks, finally leading to observed decreases in elastic modulus and compressive strength.

Another observed form of decay is granular disintegration and surface erosion (Figure 2C,F). In this sense, the graffiti appear rough in many areas, reflecting that individual mineral grains are detaching from the rock surface. Granularity and surface erosion occur due to prolonged exposure to wind and moisture, which weakens the cohesion of mineral grains, allowing them to dislodge over time. The combination of these processes in Bigeh accelerates the loss of carved details and compromises the long-term mechanical stability of the stone. To align with this mechanism, He et al. [28] demonstrated that the granular disintegration rate increases according to the water flow rate and immersion time in water, leaving large pores in the granite in various stages of disintegration. Salt crystallization further accelerates this process, as dissolved minerals in water enter the rock’s pores, crystallize, and expand, leading to internal stress and surface degradation. In addition, flaking and exfoliation are also observed, as shown in Figure 2E, where large sections of the rock surface appear to have peeled away. This type of damage is common in granite due to hydration and dehydration cycles, especially in environments where the rock is periodically exposed to and submerged in water. When water penetrates microcracks and evaporates, it leaves behind salt deposits that exert pressure on the rock surface, causing layers to detach. This process is exacerbated by fluctuating water levels in the Nile, which create cycles of expansion and contraction in the rock. Moreover, and in this context, Migon [29] emphasized that granites are highly responsive to the amount of moisture in the environment.

Additionally, biological growth and staining have been noted, as shown in Figure 2B,D, where vegetation is visible near and on the rock surfaces. The presence of algae, moss, or lichen indicates high moisture levels, which promote biological colonization. These organisms produce organic acids that chemically react with the rock minerals, weakening the surface and contributing to further erosion. Biological growth also traps moisture, increasing the rate of salt crystallization and accelerating weathering [30]. Furthermore, the impact of Nile water on these inscriptions is an essential factor in their deterioration. The proximity of these rocks to the river means they are subject to periodic wetting and drying, which significantly influences their condition. In this case, Zhao et al. [31] explained that the increasing number of wetting and drying cycles affects the properties of granite greatly, such as mass loss, color, surface roughness, and hardness. In addition, wetting and drying cycles affect the connected micropores, causing them to become more porous and more susceptible to further water penetration [32]. The presence of dissolved minerals in the Nile water, especially sulfates and carbonates, leads to chemical weathering, where these compounds react with granite minerals and weaken their structure. In this sense, Oliva et al. [33] confirmed that increasing the interactions between the granitic rocks and water affects the physical and chemical weathering rates. In areas where water flow is strong, mechanical erosion from sediment transport further contributes to surface damage.

The decay mapping and sketching of the granite surfaces carrying ancient graffiti were carried out and revealed various deterioration forms (Figure 3A–E), including diaclases (both horizontal and vertical), separation, layering, and granular disintegration. Additional decay phenomena include black crust formation, chipping, and biological impacts such as bird waste accumulation. For quantification of some decay patterns, most of the visible cracks appear to be less than 1 cm wide. In addition, some wider cracks are estimated to be 2–5 cm wide. Many layers appear to be 1–3 cm thick. Chipped areas vary in size, ranging from 5 cm to 30 cm in diameter, and the individual pittings are much smaller, estimated to be 1–5 cm in diameter. Furthermore, in some areas, the black crust covers an estimated 20–50% of the visible surface, and the bird waste areas vary in size, but some cover areas of 10–20 cm in diameter. These decay forms, influenced by environmental and hydrological factors, particularly the fluctuating levels of Nile water, contribute to the gradual degradation of the graffiti.

3.2. Microscopic and Petrographical Description

The digital microscope was utilized to reveal detailed textural and morphological characteristics of the hand samples, comparing submerged and unsubmerged specimens. Consequently, the unsubmerged granite Figure 4 (unsubmerged A,B) shows a relatively smoother and less degraded surface but still exhibits notable weathering features. Feldspar and quartz grains maintain sharper edges than their submerged counterparts, though feldspar surfaces display microcracking, likely caused by daily thermal stress and weathering cycles. In addition, oxidation is evident in the reddish-brown hues on the surface, reflecting the alteration of iron-rich minerals due to exposure to atmospheric oxygen and moisture. Quartz grains show minor etching, while biotite appears weathered and flaky, indicating oxidative and hydration processes. Unlike the submerged samples, the unsubmerged granite lacks significant biofilms or organic growth, showing limited biological influence. Finally, the impacts of environmental conditions on granite decay for the various samples are caused by water exposure driving chemical and biological alterations in submerged samples, while atmospheric exposure and thermal cycling dominate the decay processes in unsubmerged granite. Regarding the submerged granite samples in Figure 4 (submerged C,D), they display a rough, uneven surface with prominent signs of decay. Dark mineral inclusions such as biotite and other heavy minerals appear weathered, showing darkened patches and surface encrustations. Quartz grains exhibit partial dissolution, indicative of chemical processes from prolonged water exposure, while feldspar minerals show surface pitting, cracking, and alteration due to hydrolysis. Biofilms and microbial colonies seem to contribute to the encrustation and secondary mineral precipitation observed on the surfaces. Additionally, alteration halos surrounding some minerals point to chemical weathering processes, potentially forming secondary clay minerals. Consequently, the submerged granite has undergone significant decay due to prolonged submersion, leading to chemical and biological alterations.

The petrographic analysis showed mineralogy, alteration features, and decay processes from the submerged and unsubmerged representative samples. This granite is a coarse-grained rock with a primary mineralogy in both cases, composed mainly of k-feldspar (Kfs), quartz (Qz), plagioclase (Pl), biotite (Bio), and hornblende (Hbl), in decreasing order of abundance (Figure 5A,B). Magnetite and titanite are the major accessory minerals, while apatite and zircon are minor accessory minerals. The unsubmerged samples serve as standard specimens of unaltered granite. In addition to the described mineralogy, quartz grains are observed to be anhedral and intergrown with feldspars within the granitic matrix. These grains also display fractures, with microcracks propagating through the matrix (Figure 5C, red arrows). Furthermore, quartz exhibits undulatory extinction, indicating tectonic deformation and suggesting that the rock has experienced some level of stress after crystallization. K-feldspar shows a perthitic texture, which resulted from exsolution during the slow cooling process. Signs of illitization and kaolinization of K-feldspars are observed, and plagioclase shows no strong signs of alteration to sericitization (Figure 5D) but displays incipient kaolinitization, appearing cloudy. This means that weathering is affecting the feldspar, leading to the formation of clay minerals. Biotite appears relatively fresh but exhibits minor oxidation along its edges, evidenced by the darkening and fine iron oxide precipitates, and also partial chloritization that is evident from a greenish hue. Further, in the submerged samples, quartz appears as anhedral grains and remains stable with no significant alteration and shows undulatory extinction (Figure 5E) and/or contains microfractures (blue arrows, Figure 5F), as in unsubmerged samples (Figure 5C). K-feldspar exhibits greater signs of illitization (Figure 5G), indicating an interaction with potassium-bearing fluids that led to the formation of fine-grained mica. In this context, Yuan et al. [34] added that feldspar can display mixed wettability and can be altered by precipitation of an electrostatically charged clay coating on the feldspar surface. Plagioclase is also partially altered, with initial signs of kaolinization along its cleavage planes, forming cloudy textures due to the breakdown of feldspar into clay minerals. In this sense, Papoulis et al. [35] explained that kaolinization can happen in four progressive stages and each stage is characterized by the appearance or disappearance of kaolinite crystals with discrete morphology and composition. In addition, they added that kaolinite displays an Al-decreasing, Fe-increasing trend, following the sequence of appearance of the morphological forms with advancing weathering such as flaking. Biotite displays incipient chloritization that is evident through a change in pleochroism from brown to green and exhibits the strongest oxidation to iron oxides in terms of the unsubmerged samples (Figure 5H).

Under SEM, unsubmerged samples showed differences due to the environmental conditions. In Figure 6A,B, the crystals show a rough and irregular surface with prominent intercrystalline cracks (red arrows). These features are indicative of physical weathering, primarily caused by thermal stress from temperature fluctuations and moisture cycling due to their proximity to the Nile River, contributing to granular disintegration (Figure 6C,D). Individual mineral grains are loosening from the stone matrix, a process exacerbated by water infiltration that weakens the bonds between crystals. The fractured appearance of feldspar grains points to hydrolysis, a chemical weathering reaction where silicate minerals break down in the presence of water. The overlapping microcracks in these zones further facilitate material loss. Additionally, Figure 6E shows cubic halite crystals, confirmed by the EDS spectrum (Figure 6G). The presence of halite indicates salt crystallization from the evaporation of Nile water, which exerts pressure within pores and fissures, contributing to surface flaking and granular exfoliation as well. Sulfur (S) was also detected, probably indicating sulfate-based compounds, which likely result from the interaction of the granite with atmospheric pollutants or/and natural sources such as the Nile River which are rich in sulfates. In that case, sulfates can combine with calcium to form gypsum, a soluble salt that can also contribute to granular disintegration and surface scaling [36]. Furthermore, Figure 6F confirms the formation of biofilms or biological residues on the surface, contributing to biochemical weathering. Microorganisms, such as algae or lichen, may have colonized the granite, producing organic acids that dissolve silicate minerals. These acids etch the surface, creating pits and further exacerbating decay.

Figure 5. Main mineralogy and textures of this unsubmerged (A,B) and submerged granite (E); intercrystalline microcracks in both unsubmerged (red arrows, (C)) and submerged granite (blue arrows, (F)); replacement and/or alteration of feldspars and plagioclase to form clay minerals in unsubmerged (D) and submerged granite (G); example of oxidized biotite (H). Microphotographs C and H were taken with parallel nicols. Legend: Qz: quartz; Ab: albite; Mcc: microcline; Bio: biotite. Green scale bar represents 1 mm. Mineral symbology according to [37].

Figure 5. Main mineralogy and textures of this unsubmerged (A,B) and submerged granite (E); intercrystalline microcracks in both unsubmerged (red arrows, (C)) and submerged granite (blue arrows, (F)); replacement and/or alteration of feldspars and plagioclase to form clay minerals in unsubmerged (D) and submerged granite (G); example of oxidized biotite (H). Microphotographs C and H were taken with parallel nicols. Legend: Qz: quartz; Ab: albite; Mcc: microcline; Bio: biotite. Green scale bar represents 1 mm. Mineral symbology according to [37].

The detection of phosphorus (P, Figure 6H) assures biological activity or chemical wastes that could be from agricultural activities. In this context, phosphates can originate from organic matter, such as decaying vegetation or biofilm activity on the stone’s surface. These biofilms release organic acids that dissolve silicate minerals, promoting chemical weathering. The presence of P may also reflect exposure to bird guano (Figure 3B,D), and under SEM is characterized by a plate-like structure (Figure 6D). In this sense, Hernández et al. [38] explained the possibility of phosphates in their case study due to biological and vegetational actions, confirming the significant impact of phosphates on granite discoloration, disintegration, and loss of material. Moreover, some crystals of calcite were detected, indicating the precipitation of carbonates from calcium-rich groundwater or Nile River water interacting with atmospheric CO₂.

On the other hand, microtextural and chemical analysis of the submerged granite sample shows surface features indicative of microcracking (red arrows), micropitting, granular disintegration, and exfoliation (Figure 7A–D, respectively), exacerbated by the persistent presence of water. The cyclic wetting and drying associated with water-level fluctuations promote dissolution and recrystallization of mineral phases, leading to structural weakening. Additionally, the rounded and eroded edges visible in some areas are caused by the ongoing mechanical weathering due to sediment transport and abrasion from flowing and fluctuating water. Biological activity is also evident in the intricate filament-like structures observed in Figure 7C,E (mainly filaments, green arrow). These bio-structures likely correspond to microbial colonies or biofilms that thrive in the submerged conditions. Such biofilms secrete organic acids that dissolve silicate minerals, exacerbating chemical decay and biogenic weathering. For instance, Abdel-Satar et al. [39] confirmed the presence of various types of bacteria due to fecal contamination in the Nile River. The EDS spectrum from Figure 7E highlights the presence of different elements which correspond to organic material and clays (Figure 7G). In this context, Vlasov et al. [40] demonstrated that the biofilm can infiltrate into cracks and pores, and its growth exerts pressure on the structural components of granite, affecting individual crystals within the stone, in addition to its role in granite surface leaching due to its chemically active compounds. On the other hand, this clay not only is a product of the argillization of feldspars but also contains suspended materials and sediments from the Nile, which act as contaminants. In the Aswan-Sohag traverse, these contaminants have been identified and classified into eight distinct genetic particle types, such as biogenous–aeolian (or silica), terrigenous (Fe–aluminosilicate), authigenic (calcium carbonate), biogenous (apatite), authigenous–terrigenous (Fe–oxyhydroxide–montmorillonite), diagenetic (iron–sulfide), terrigenous (titanium oxide), and authigenous (Mn-Fe–oxyhydroxide) [41]. Mohallel [42] analyzed the groundwater of one of the aquifers in Aswan and detected that the salinity of the groundwater is 17%, and encountered the presence of NaCl, MgCl₂, MgSO₄, CaSO₄, and Ca (HCO₃)₂ salts. In the same context, Olsen and Kome [43] explained that at an annual inflow of 55 km³, the salt influx reaches 14 million tons. These salts can be infiltered and dissolved into the Nile River, causing its contamination in Aswan generally. Finally, Figure 7F shows the presence of elongated remnants of diatoms in various forms and points to localized zones of biodeterioration on granite surfaces. In this context, in the freshwater of Egypt and the Nile River in some localities, various diatom assemblages were detected, such as Cyclotella meneghiniana, C. ocellata, Cocconeis placentula, Melosira granulata, Nitzschia palea, N. obtuse, and N. obtusa var. scalpelliformis [44]. In this microphotography, a unique crystal of baritine was observed as well (purple arrow and elements “S+Ba” in EDS spectra, Figure 7H).

3.3. Mineralogical Composition

X-ray diffraction (XRD) confirmed the mineralogical composition of both the submerged and unsubmerged granite samples (Figure 8). Quartz (Qz), albite (Ab), and microcline (Mcc) appear as the most abundant minerals and are in similar proportions. Biotite (Bio) exhibits a relatively stable presence across the samples, although chlorite (Chl) and hornblende (Hbl) appear predominantly in submerged samples. Except for chlorite, no other phyllosilicates resulting from the alteration of other minerals were detected, maybe due to their low concentration, as well as the possible presence of oxides observed in optical microscopy, for example, from the oxidation of biotite. These minor differences could indicate that prolonged submersion may influence the composition and relative abundance of certain minerals, but this could also be due to variability in the granite itself. However, the chemical composition obtained by XRF would reveal this difference, since the submerged samples present a slightly higher percentage of Fe, a product of this oxidation (

Table 2. Chemical compositions of the unsubmerged and submerged samples of the major (in %) and trace (in ppm) elements and the standard deviation of each value.

	Major Element (in %)			Trace Element (in ppm)
	Unsubmerged	Submerged		Unsubmerged	Submerged
Al	6.507 ± 0.113	5.816 ± 0.103	Ba	280 ± 20	490 ± 20
Ca	1.738 ± 0.033	1.778 ± 0.034	Cr	80 ± 20	160 ± 20
Fe	3.491 ± 0.024	4.972 ± 0.027	Mn	190 ± 50	740 ± 50
K	3.305 ± 0.029	3.216 ± 0.029	Nb	50 ± 10	60 ± 10
Mg	0.288 ± 0.151	0.381 ± 0.147	Rb	80 ± 10	60 ± 10
P	0.156 ± 0.019	0.549 ± 0.137	Sr	240 ± 10	190 ± 10
Ti	0.474 ± 0.007	0.421 ± 0.008	V	110 ± 30	150 ± 40
Si	39.605 ± 0.131	32.628 ± 0.129	W	80 ± 30	60 ± 30
Bal	44.274 ± 0.162	49.975 ± 0.146	Zn	90 ± 10	120 ± 10
			Zr	350 ± 10	520 ± 10

), which is typically leached out under prolonged water exposure. In addition, this alteration process produced decreases in Si and Al, and an increase in P (organic origin) with respect to the major elements, while for the minor elements there are notable differences in Ba, Cr, Mn, Sr, and Zr, and the action of water responds to this mobility of elements by means of oxides–hydroxides and/or sulfates. In this regard, these chemical results confirmed the impact of hydrochemical weathering on submerged granite. For this, prolonged exposure to the Nile River, with its fluctuating sediment load and contaminant levels, accelerates mineral transformation through ionic exchange, oxidation, and biogeochemical interactions. In addition, the presence of organic matter and dissolved ions in river water may further influence weathering intensity by promoting mineral dissolution and recrystallization. Finally, integrating sediment movements and river contamination levels provided a clearer picture of how aquatic environments drive granite degradation beyond natural lithological variability.

3.4. Safeguarding and Conservation Plan

Preserving the ancient granite stelae of Bigeh Island, which features graffiti from the reign of Khaemwaset, requires a well-structured approach that balances immediate stabilization with long-term conservation. The primary objective is to mitigate existing damage, slow ongoing decay, and protect these archaeological monuments from future environmental threats. The conservation process begins with a thorough on-site condition evaluation. This includes visual inspections, high-resolution photography, petrological analysis, microscopic and chemical analysis, and detailed decay mapping to document current issues such as cracks, exfoliation, and granular disintegration. These initial steps are essential for evaluating the stelae’s present condition and forming the basis of a conservation plan, as shown in the current paper. Fragile structural sections should be temporarily prioritized for structural support using wooden or metal braces, as well as scaffolding, to prevent collapse and ensure worker safety during conservation activities. The choice of support material depends on the structure’s size, weight, and material composition, with wooden braces offering flexibility and ease of adjustment, while metal scaffolding provides robust, long-term stability.

Additionally, loose debris and biological materials, such as bird waste and vegetation, are carefully removed using soft brushes and low-pressure air to prevent further surface abrasion. This careful cleaning prepares the stelae for subsequent preservation measures, ensuring that immediate risks are addressed while laying the groundwork for long-term protection. In areas affected by salt crystallization, a gradual desalination process must be initiated. Damp cotton pads or clay poultices (like kaolin or sepiolite), soaked in deionized water, are carefully applied to draw out soluble salts through capillary action. This technique minimizes the risk of salt-induced damage, such as subfluorescence or surface scaling, and serves as a preliminary step before more intensive desalination treatments. The pads are regularly monitored and replaced to prevent reabsorption of extracted salts, ensuring a thorough and controlled cleaning process. This process is repeated until salt levels drop to safe thresholds. After desalination, a silicate-based consolidant is applied in cycles to reinforce weakened grain boundaries, enhancing structural durability. In this sense, repairing larger cracks by injecting reversible fillers and detached fragments using specialized adhesives should also be considered, ensuring proper alignment and minimal visual impact. Additionally, small cracks and surface fissures should also be sealed with a reversible, low-viscosity product, such as ethyl silicate, to prevent further propagation and structural weakening. This process must be carefully executed to ensure the consolidant penetrates deeply into the stone matrix, reinforcing the material without compromising its archaeological texture. To protect against future decay, surface treatments are introduced. A breathable, reversible hydrophobic coating is applied to reduce water infiltration while allowing moisture exchange.

To mitigate environmental impact, protective shelters made from UV-resistant tarps or lightweight modular structures are installed to shield the stelae and other vulnerable elements from direct sunlight, rain, and wind-driven debris. These shelters help regulate microclimatic conditions, reducing thermal fluctuations, moisture infiltration, and the risk of sudden temperature-induced fractures. Finally, long-term preservation relies on continuous monitoring and periodic maintenance, considering the installation of sensors to track environmental variables such as humidity, temperature fluctuations, and salt accumulation, and carrying out regular inspections and touch-up treatments ensures early detection of emerging decay, enabling timely interventions.

4. Conclusions

The present study highlighted the environmental impact, particularly the fluctuating water levels of the Nile River, on the long-term stability of the ancient granite surfaces bearing graffiti at Philae Archaeological Site (Aswan, Egypt).

The mineralogical analysis confirmed that this granite exhibits varying degrees of alteration due to prolonged exposure to environmental impacts. Notably, there is alteration of feldspars to form clay minerals in response to water interaction, while biotite displays oxidation, which further contributes to microstructural weakening. These transformations could contribute to altering the physical and chemical stability of the granite, making it more susceptible to decay over time. This study also confirmed that submerged granite samples exhibit greater mineralogical alterations compared to unsubmerged samples, which reinforces the role of water-related processes in stone deterioration due to the impact of cyclic wetting and drying on the granite surfaces, particularly in areas frequently exposed to the Nile’s fluctuating water levels. These cycles also promote salt crystallization, hydrolysis, and mechanical stresses that accelerate the detachment of mineral grains, leading to granular disintegration and favoring surface exfoliation and layering. Additionally, the presence of soluble salts such as sodium chloride and sulfate, which infiltrated the stone’s pores and, upon crystallization, led to internal pressure that exacerbates microcracking and scaling, further weakens the rock structure. Additionally, the presence of sulfur in the submerged samples confirms the influence of sulfate-rich water, which accelerates the dissolution of feldspar minerals and contributes to surface roughness and pitting. Furthermore, biological colonization plays a vital role in the decay processes observed on both submerged and unsubmerged granite surfaces. Using SEM, this study identified biofilms, diatoms, and organic residues, which indicate the active microbial involvement in stone degradation. These microorganisms secrete organic acids that chemically interact with minerals, which results in dissolution and increases weathering effects. The presence of phosphorus in the EDS analysis supports the hypothesis that biological activity, along with external environmental factors such as agricultural runoff, birds’ wastes, and atmospheric pollutants, contributed to the degradation of the granite surfaces. Moreover, thermal stress caused by temperature fluctuations could also contribute to increasing the microfractures in the rock, which, over time, propagate and contribute to the loss of inscribed surfaces. This effect is particularly pronounced in unsubmerged samples, where repeated exposure to intense solar radiation during the day, followed by rapid cooling at night, leads to progressive structural fatigue and increased susceptibility to environmental damage.

Urgent conservation efforts are required to mitigate further deterioration of the granite graffiti. Potential conservation strategies should include the implementation of protective measures to reduce direct exposure to fluctuating environmental conditions, the application of desalination treatments to remove harmful soluble salts, and the development of controlled water management strategies to minimize prolonged submersion of these inscriptions. Additionally, biofilm removal techniques should be employed to address biological colonization while preserving the durability of the rock surfaces.