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https://www.researchgate.net/profile/Elena-Crespo-Feo?enrichId=rgreq-62f94bbc4e14f42942b71069c8cd8e41-XXX&enrichSource=Y292ZXJQYWdlOzM3OTU0NzgxNztBUzoxMTQzMTI4MTMwNTg2MTE4NUAxNzM4MDY0MDAwMjIx&el=1_x_7&_esc=publicationCoverPdf https://www.researchgate.net/profile/Mario-Iglesias-Martinez?enrichId=rgreq-62f94bbc4e14f42942b71069c8cd8e41-XXX&enrichSource=Y292ZXJQYWdlOzM3OTU0NzgxNztBUzoxMTQzMTI4MTMwNTg2MTE4NUAxNzM4MDY0MDAwMjIx&el=1_x_10&_esc=publicationCoverPdf Vol.:(0123456789) Environmental Earth Sciences (2025) 84:85 https://doi.org/10.1007/s12665-024-12008-z ORIGINAL ARTICLE Chromatic evolution, chemical changes, and biological colonisation in the quarry fronts of the Santullán limestone massif (Cantabria, Spain): implication for the mitigation of visual impact in mountain quarrying Mario Iglesias‑Martínez1,5 · Jorge Fernández‑Suarez2 · Asunción de los Ríos2 · Xabier Arroyo3 · Mari Luz García‑Lorenzo4 · Elena Crespo‑Feo4 · Chloe Plet5 · Pedro De Andrés6 Received: 24 March 2024 / Accepted: 30 November 2024 © Crown 2024 Abstract The visual impact of the chromatic contrast between quarry faces and rocky outcrops represents one of the prominent dis‑ turbances to natural environments. This study, therefore, aims to quantify color changes over time in quarries by analyzing three faces of an active limestone quarry in Santullán, Cantabria, that were exposed to atmospheric conditions in 1978, 2003 and 2021. To achieve this, the contribution of biological colonisation to natural darkening, along with the physicochemical changes occurring on the quarry faces, have been evaluated using scanning electron microscopy in secondary and backscat‑ tered electron mode, UV–Vis spectrophotometric techniques, Raman spectroscopy and XRD and XRF analysis. The analysis revealed that the color change was primarily due to microbial colonisation rather than oxidative chemical reactions. Although color change does not follow a direct and progressive relationship with exposure time, biological colonisation, identified primarily as microbial communities dominated by phototrophic microorganisms, shows a clear increase in microbial pres‑ ence, bioalteration, and penetration into the rock substrate in older samples. The most significant visual changes appear to occur during the first years of exposure of the massif to atmospheric conditions. Keywords  Quarrying visual impact · Rock color characterisation · Biological colonisation · Endolithic microorganism · Bioweathering * Mario Iglesias‑Martínez m.iglesias@igme.es; mario.iglesias-martinez@csiro.au Jorge Fernández‑Suarez j.fernandez@igme.es Asunción de los Ríos arios@mncm.csic.es Xabier Arroyo xarroyo@geo.ucm.es Mari Luz García‑Lorenzo mglorenzo@ucm.e Elena Crespo‑Feo ecrespo@ucm.es Chloe Plet chloe.plet@csiro.au Pedro De Andrés pedro.deandres@santullan.es 1 CSIC‑Centro Nacional Instituto Geológico y Minero de España, Unidad de Oviedo, C/Matemático Pedrayes, 25, 33005 Oviedo, Asturias, Spain 2 CSIC-Museo Nacional de Ciencias Naturales, C/Serrano, 115b, 28006 Madrid, Spain 3 Centro de Asistencia a la Investigación de Técnicas Geológicas, Universidad Complutense de Madrid, José Antonio Novais 2, 28040 Madrid, Spain 4 Departamento de Mineralogía y Petrología, Universidad Complutense de Madrid (UCM), 28040 Madrid, Spain 5 Mineral Resources, CSIRO, 26 Dick Perry Avenue, Kensington, WA 6151, Australia 6 Canteras de Santullán, Lugar Barrio Santullán, 50, 39706 Santullán, Cantabria, Spain http://crossmark.crossref.org/dialog/?doi=10.1007/s12665-024-12008-z&domain=pdf Environmental Earth Sciences (2025) 84:85 85   Page 2 of 19 Introduction Open-cast mining sites contrast in many ways, one of which is that this type of mine often stands out in the landscape (Fig. 1). Environmental remediation at mine closure usually tackles removing contaminants from envi‑ ronmental media such as soil or water. However, it can also encompass the restoration of the natural landscape. Landscape aesthetics is the enjoyment and pleasure of observing environmental scenery (Swaffield and McWil‑ liam 2013). As such, a landscape's perceived beauty can impact the well-being of a population (Tribot et al. 2018). Quarry fronts dramatically alter the landscape as they pro‑ duce significant differences in morphology (type of slope, vertical slopes, distribution in benches, etc.) and color compared with the natural environment. Rock fronts, when exposed to meteoric conditions, are impacted by external environmental factors (i.e., atmos‑ pheric weathering, humidity, biological colonisation), which lead to progressive chromatic variations through time. Commonly, this change consists of a darkening of the rocky material (Grossi et al. 2006). A comparative study of the chromatic coordinates, luminosity, hue, and chroma from different samples makes it possible to objectively estimate the color variations seen on the rock surface (comparing fronts opened at different times) and evaluate the rates of the temporal evolution of these changes. These color variations are usually attributed to the degree of oxidation of chromophore elements contained within min‑ erals and their concentrations (Benavente et al. 2003). Iron (Fe) is the most widespread and impactful chromophore ele‑ ment in rock surfaces and settings. Mineral phases with fer‑ ric material produce a red-brown color in the stone, whereas reduced phases lead to a blue-black shade. When Fe-bearing rocks are exposed to the atmosphere, for instance, after blast‑ ing, many redox reactions occur to achieve equilibrium. For this reason, reduced phases change color quickly, whereas oxidized phases remain generally stable during exposure to weathering (Benavente et al. 2003). Mineralogical and Fig. 1   A The north and east fronts of the Santullán pit show the great visual impact of the quarry. B, C The Western half of the unaltered Santul‑ lán massif developing karren forms and other karstic morphologies Environmental Earth Sciences (2025) 84:85 Page 3 of 19  85 geochemical analyses of the surface patinas of the three quarry faces were carried out using X-ray fluorescence (XRF) and scanning electron microscopy (SEM) to quan‑ tify chromophore elements. However, redox reactions of chromophore elements are not solely responsible for the changes of color observed. Several studies have shown that colonisation of the quarry fronts by lichens, cyanobacteria, and other microbial communities also plays a key role in color variations through time (Prieto et al. 2005; Monzó and García del Cura 1999). The lichens and microbial com‑ munities can exert physical forces on the colonized rock that cause structural damage to the rock surface. Additionally, the organic acids they produce, particularly oxalic acid, can dissolve minerals and chelate metallic ions (e.g., Chen et al. 2000), leading to changes in color. Thus, these microbial colonizers of the lithic substrate, known as lithobiontic microorganisms, are involved in biogeochemical and biogeo‑ physical processes that contribute to the disintegration and dissolution of minerals and rocks (Ascaso and Wierzchos 1995; De los Ríos and Ascaso 2005). Therefore, characteriz‑ ing the dynamics and complexity of biological colonisation is essential for understanding its contribution to the varia‑ tions in textures and colors compared to the surrounding massif. The morphological characteristics of mountain quarries (type of slope, vertical slopes, distribution in benches, etc.) make it challenging to use traditional revegetation tech‑ niques commonly used to mask the visual impacts in mines and quarries in less steep terrain. More and more experts (Martín Duque et al. 1998; Prieto et al. 2005), consider that restoration procedures based on the evolution of natural sys‑ tems and their capacity for self-regeneration (rather than those based on revegetation processes) should be favored. To this end, knowledge of the causes of color changes in quarry faces is fundamental when managing and planning the actions to be carried out, whether these are interventionist (e.g. favoring biological colonisation) or non-interventionist. To this end, quarries are an ideal natural environment, as the information obtained is directly applicable to the place where it will be implemented. The exposed rock surfaces are of known age, making it easier to calculate temporal rates for the development of weathering processes. To propose actions to correct the visual impact associ‑ ated with the chromatic contrast between the quarry faces and the outcrops of the massif, a detailed review of tech‑ niques and cases applied in mining operations has been car‑ ried out to evaluate their possible application in the case of the Santullán quarry (Cantabria, Spain). The present study characterises the surfaces of the unaltered carbonate massif and analyses the evolution through time of the quarry fronts opened in 1978, 2003 and 2021. In particular, the color vari‑ ations between these three quarry fronts were characterized using (1) statistical analysis based on chromatic parameters for each quarry front, (2) mineralogy and geochemistry, and (3) micro-ecosystem characterization. Geology and natural environment Santullan massif is located in the Basque-Cantabrian Basin in the domain of the Basque Arc (Miró et al. 2020). Cal‑ careous units of Aptian and Lower-Middle Albian age are the backbones of the landscape and rest on a detrital series. These calcareous and detrital rocks reach a total elevation of about 800 m a.s.l., constituting the relief known as Peña de Santullán. The stratigraphical series is composed at its base of a stretch of bioclastic calcarenites, which are grey and well-stratified. The middle section is made up of compact loams with intercalations of clayey limestones and calcar‑ enites and, finally, the upper section is made up of massive limestones and calcarenites, locally dolomitized, with rud‑ ists, corals and bryozoans. The upper massive limestone is the rock Canteras de Santullán S.A. exploited to produce high-quality calcium carbonate for industry. Its lithology and tectonic features determine the land‑ scape of the Peña de Santullán. The hill range stands out for its steep crests and the development of karsts. A large part of the slopes of the massif are denuded terrain with numerous karstic Karren showing needles or pinnacle shapes (Fig. 1) and several lines. The study area has a temperate-humid climate, with prac‑ tically no dry season (Koppen Climate Cfb). Precipitation is regular throughout the year, except in June, July, and August when precipitation values drop to about half of the rest of the year. Annual rainfall varies between 800 and 1300 mm. The air temperature is relatively uniform, with annual averages between 13 and 17 °C. There is almost no frost nor tempera‑ tures above 30 °C throughout the year (Fig. 2). Methodology The characteristics of the limestone of the Santullán mas‑ sif have been defined about all aspects that may influence the color variations of their exposed surfaces—i.e., type of rock, mineralogical composition, textures, crystalline hab‑ its, microporosity, presence of alterable minerals, biologi‑ cal colonisation. Other aspects are likely to have relevance both in the physicochemical degradation processes of the rock and intervene in the surface's susceptibility to support biological colonisation. Surface fragments were sampled from three quarry faces: one recently opened (S-2021) with a fresh surface, and two others exposed to weathering for two and four decades, respectively (S-2003 and S-1978) (Figs. 3, 4). Environmental Earth Sciences (2025) 84:85 85   Page 4 of 19 Petrological characterization Four thin sections from limestone samples representative of the main facies in the Santullán quarry were made for petrographic characterisation. The petrographic studies have been carried out using a petrographic microscope, model Zeiss Primotech, equipped with the software Lab‑ scope Mat to process the digital images on 30 microns thin sections without lacquering and with a third of the film stained with red alizarin. The petrographic characteristics of the studied thin sections allowed us to distinguish two main types of limestone typologies; according to the dif‑ ferent classifications, they can be interpreted as biosparites and biomicrites (Folk's classification 1959) or as bioclas‑ tic grainstone and packstone (according to Dunham's Fig. 2   Main plant species present in the undisturbed part of the mas‑ sif. A Eucalyptus plantations at the foot of the massif on the ascent to the eastern face of the quarry; B isolated masses of holm oaks on the southern slope; C grassy meadows at the top of the central part of the massif; D specimen of Quercus trees on the crags of the Peña; E colonisation of the thick fragment glacis by vegetation belonging to the Araliaceae family (ivy); F example of flora developed in small crevices on a vertical cliff Environmental Earth Sciences (2025) 84:85 Page 5 of 19  85 classification 1962). The Folk’s classification terminology describes the material throughout this manuscript. Chemical analysis by X‑ray fluorescence A hand-held, high-performance X-MET8000 Expert Geo portable X-ray fluorescence (XRF) elemental analyzer was used for non-destructive chemical analysis of the rock of three fragments taken from quarry faces exposed at different dates (1978, 2003, and 2021) to recognize compositional changes associated with the effects of weathering on the surfaces. Five measurements per sample were carried out to increase the representativeness, considering the surfaces' heterogeneity and this technique's limitations, which pro‑ vided semi-quantitative results. Color determination by UV‑Vis spectrophotometry A portable KONICA MINOLTA CM-700d spectropho‑ tometer, equipped with a xenon pulsed light lamp with a UV filter and a detector consisting of a silicon photodiode array, was used for color determination. These techniques permit the quantification of the color parameters of the different samples. Three transect readings were taken from each test specimen to measure the different chro‑ matic parameters (Fig. 4). The readings were taken with a spacing of 0.5 cm along each line. The measurement con‑ ditions set in the apparatus were: viewing aperture diam‑ eter 3 mm (SAV mode), illuminant D65, and observer 2° (CIE 1932) with an illumination viewing geometry d = 8°. Surface conditions can influence the color and appearance Fig. 3   Sampling locations at the fronts opened in 1978 (A, B) and 2003 (C, D). Stars indicate the sampling points. Note the abrupt vari‑ ation in color at the 1978 front between the exposed area, which has developed a dark surface patina (on the top), and the bottom part, where the abrasion of stockpiles accumulated has removed that patina Environmental Earth Sciences (2025) 84:85 85   Page 6 of 19 of objects. Humans perceive colors by the light reflected off an object, and the different surface conditions reflect light differently. There are two ways how light reflects off an object and they are referred to as specular reflection and diffuse reflection. Specular reflection occurs when light reflects at an angle equal to but opposite the angle of incidence from the light source. This reflection occurs strongly on objects with glossy, smooth surfaces. When the reflected light is scattered in many directions, it is called diffuse reflection, and this reflection occurs strongly on objects with matt or irregular surfaces. Since the surface of limestone samples is either not fully reflective or matt, including or excluding the specular com‑ ponent may be essential for color measurements. There‑ fore, measurements were performed simultaneously in the specular component included (SCI) and specular component excluded (SCE) modes. Before the measurements, a zero calibration was per‑ formed by taking five shots with the device at least 1 m away from any surface, and a white calibration was performed with the manufacturer's supplied part attached to the tar‑ get. Data acquired with the CM-700d spectrophotometer require very little processing, as calibration is applied to the data during acquisition. The data is displayed visually during acquisition as graphs of values, spot color spectra, and sample color simulation on Geotek XRF capture pro‑ gram screen. The colorimetric values obtained are RGB color coordinates, L*a*b*, XYZ, Munsell data and spectral reflectance for wavelengths from 400 to 700 nm (in 10 nm increments). Scanning electron microscope and X‑ray diffraction analysis Rock fragments of the same samples were also studied by scanning electron microscopy (SEM), using a JEOL JSM- 820 electron microscope working at 20 kV, with a resolution of 35 Å. Secondary electron and backscattering detectors were used. EDS chemical analysis was applied to ascertain the nature of the investigated areas. SEM observations were conducted on sample fragments placed on conductive car‑ bon tape attached to the sample holders. The samples were sputter-coated with gold. Bulk mineralogy was determined by powder X-ray dif‑ fraction (XRD), employing a Bruker D8 Advance diffrac‑ tometer with a Sol-X detector and Cu (Kα) radiation. Rock fragments were placed directly into XRD holders, and the flat patinas were exposed to the X-ray to compare the sur‑ faces with natural patinas. Some rock samples were processed using the ‘SEM-BSE technique’ by Wierzchos and Ascaso (1994). Briefly, bio‑ logically colonized rock fragments were fixed in glutaralde‑ hyde and osmium tetroxide solutions, dehydrated in a graded ethanol series, embedded in LR White resin, and finely pol‑ ished. The samples were observed using a FEI INSPECT microscope after being carbon coated. Fig. 4   Surface of the samples analysed by the spectrophotometer with an indication of the transects used to measure the different chromatic parameters. Sample S-2003 (A), sample S-1978 (B), and sample S-2021 (C) Environmental Earth Sciences (2025) 84:85 Page 7 of 19  85 Micro‑Raman spectroscopy analysis The micro-Raman spectra of samples S-1978 and S-2003 were obtained in a Thermo-Fischer DXR Raman Micro‑ scope at the Museum of Natural Science- Spanish National Research Council (CSIC) in Madrid (Spain). It and a 532 nm laser source delivering 10 mW at maximum power at the sample, with the 50X long working distance objective of the confocal microscope due to the irregular surface of the samples. The average spectral resolution in the Raman shift ranging from 200 to 1800 cm−1 was 4 cm−1, with 900 lines/ mm grating and 1.2 µm spot size. The system was operated under OMNIC 1.0 software fitting working conditions such as a pinhole aperture of 25 µm and an average of ten expo‑ sures timed at 0.5 s each to avoid fluorescence effects. Results Color differences are often measured using CIELAB sys‑ tems (CIE L*a*b*) because they better represent human sensitivity to color than other color-coding systems (Grossi et al. 2006). The definition of color is based on three dimen‑ sions: hue, chroma (saturation), and lightness. Chromatic‑ ity includes hue and chroma, specified by two chromaticity coordinates. The lightness factor must also be included to identify the sample's color accurately. The three parameters defining the color must be the same for two colors to be the same. The use of the CIELAB system allows the estima‑ tion of the three classical color parameters: "L*," "a*" and "b*," where "L*" represents the lightness, "a*" represents the position between red and green on the axis between red (þ) and green (2), and "b" represents the position between yellow and blue on the axis between yellow (þ) and blue (Prieto et al. 2010). The three parameters are represented on three orthogonal axes in a Cartesian coordinate system (Fig. 5). The attributes of chroma ("C": saturation or color purity) and hue ("h": ab referred to as the color wheel) have been calculated using the following equations: 1. C = ( a 2 + b 2 ) 1∕2 2. h = arctan(b2∕a2) C* and h changes are more sensitive to changes in a* or b* depending on the material's original color. For example, rocks with creamy or yellowish tones, such as limestones, have values of b* much higher than those of a*. In that case, C* is strongly influenced by the b* coordinate, while h is very sensitive to changes in a* (Grossi et al. 2006), as seen in Table 1. In addition to the above parameters, the greyscale Fig. 5   Illustration of the coordinates in the CIE L*a*b* color space (left) and the color tolerances (right) Table 1   Average values of the chromatic coordinates (CIE La*b*) and of the chroma (C*ab) and hue (hab) calculated for the three sam‑ ples S-2021 S-2003 S-1978 L* Mean 46.71 26.94 33.26 SD 0.65 2.09 1.16 a* Mean 4.77 2.47 2.36 SD 0.18 0.1 0.07 b* Mean 12.21 6.75 7.57 SD 0.39 0.28 0.2 C*ab 13.11 7.8 7.94 hab 1.42 1.44 1.47 Environmental Earth Sciences (2025) 84:85 85   Page 8 of 19 reflectance, the reflectance as a function of wavelengths of the visible spectrum, and the coordinates of the Munsell system of the color specification were recorded for the three samples analyzed, all shown in Table 2. Reflectance is expressed as a percentage and measures the amount of light reflected by a surface. This parameter has been measured for the different wavelengths of the visible spectrum (400–700 nm) with increments of 10 nm in the three study samples (Table 3). As shown in Fig. 6, the high‑ est reflectance corresponds, as expected, to the sample repre‑ senting the fresh cut in the rock. The crystalline character of the rock produces a considerable reflection of incident light compared to the altered and partially biologically colonized surfaces, which represent much less reflective surfaces. Color differences between the different samples, the total color difference (ΔE*) was calculated. The total color differ‑ ence (ΔE*) was calculated to quantify the color differences between the samples. The corresponding equation is: ΔEab * = [ΔL*2 + Δa*2 + Δb*2]1/2. Mineralogical characterization of sample patinas Surface patinas are similar in all the samples described (Fig. 7). The main component of front surfaces is calcite, except for some crystals of Fe-oxides and clay minerals, occupying the porosity of the rock, which are also common in fresh rock. The presence of Ca-oxalate could not be con‑ firmed by energy dispersive X-ray (EDS) analyses. Based on the shape of some crystals, a possible earlier deposition of Ca-oxalate and a later transformation into calcite cannot be excluded. This transformation of Ca-oxalate into calcite by lichens and algae was previously suggested by Verrecchia et al. (1993). Still, no signal of Ca-oxalate was observed by Raman spectroscopy. The highest intensity Raman band of whewellite (CaC2O4 H2O) and weddellite (CaC2O4 2H2O) is usually expected at circa 1463 and 1476 cm−1, respec‑ tively. No signal at these positions has been observed in the spectra obtained. All analyzed samples show two small but visible bands at 280 and 712 cm−1, together with a sharp and well-developed peak at 1085 cm−1, corresponding to those related to calcite. One additional wide Raman band appears at 390 cm−1 in S-1978, where the sample surface is slightly reddish due to iron oxides, where the sample sur‑ face is slightly reddish due to iron oxide's presence. This band is characteristic of the iron oxy-hydroxide, goethite. Only in one of the analyzed spectra in S-1978, two medium- weak bands appeared at 1504 and 1148 cm−1, which could be related to a red/orange carotenoid pigment, β-carotene. Edwards et al. (2015) defined the 1155 and 1522  cm−1 bands as markers for β-carotene and a 1003 cm−1 band of weaker intensity. In S-1978, the higher wavenumber band is slightly displaced, and the weak feature at 1003 cm−1 was not observed. In both samples 1978 and 2003, two broad and intense bands at circa 1340 and 1580 cm−1 are present in exposed surfaces that show a blackish dye. These bands are relatively close to those related to black-bluish pigments such as gloeocapsin or scytonemin. Both UV-protective pig‑ ments are highly specific for cyanobacteria, therefore we can expect their presence in the endolithic colonies. Gloeocapsin shows its characteristic Raman bands at 1665, 1575, 1378, 1310, and 465 cm−1 (Němečková et al. 2021), whereas the four major diagnostic Raman bands of scytonemin appear at 1590, 1549, 1323 and 1172 cm−1 (Jehlicka et al. 2023). All the analyzed spectra only showed the two previous bands (1340 and 1580 cm−1) and not any of the strongest bands for either gloeocapsin or scytonemin pigment. Even when their presence cannot be disregarded, we think this correlates well with the possible presence of organic matter, as it can be attributed to (C–C) ring vibrational modes, known as the D- and G-bands of amorphous sp2 carbon. Geochemistry of rock surfaces The concentrations of major elements and trace elements in the samples are shown in Table 4. The concentrations of the major chemical elements analyzed were higher in the fresh rock surface than in the exposed rock, which developed a patina, particularly for calcium, potassium, and iron. In con‑ trast, the analysis from the S-1978 sample showed a relative enrichment of sulfur and most metallic elements (Mn, Ni, Zn, As, Se, Mo, Ag, Cd, Sb, Hg, Pb, etc.). Chemical analysis by X‑ray fluorescence The result values, expressed in percentage, are presented in Table 5. Instrument performance was optimal for elements from Z = 19 onwards, and the tool's measurement error was less than 10%. However, it is worth mentioning this method's limitation for analyzing those light elements, which leaves out of the analysis the main elements of essentially biologi‑ cal origin (C, H, P, and N). Petrological characterisation The biosparites are rich in bioclasts and peloids, partially to fully micritized, with whole or smaller fragments of mol‑ lusks, ostracods, echinoderms and occasionally foraminifera (Fig. 8A, B). These facies have microsparitic cement with a clast-supported structure. The abundant fractures through the sample are filled with mosaic sparitic cement, show‑ ing euhedral to subhedral millimeter-sized crystals. On the other hand, the biomicrites are rich in bioclasts with pre‑ dominantly millimeter to centimeter fragments of rudists and bryozoans (Fig. 8C, D) with smaller fragments of mollusks, ostracods, and echinoderms. These rocks present a micritic matrix (≤ 2 μm) partially recrystallized to microsparite and Environmental Earth Sciences (2025) 84:85 Page 9 of 19  85 Ta bl e  2   V al ue s o f c ol or a nd li gh tn es s c oo rd in at es (C IE X Y Z an d C IE L a* b* ), gr ey sc al e re fle ct an ce , a nd M un se ll co lo r s ys te m fo r t he th re e sa m pl es a na ly ze d S- 20 21 S- 20 03 S- 19 78 G re y‑ sc al e Re fle c‑ ta nc e M un se ll C ol or C IE X Y Z C ol or S pa ce C IE L *a *b * C ol or Sp ac e G re y‑ sc al e Re fle c‑ ta nc e M un se ll C ol or C IE X Y Z C ol or S pa ce C IE L *a *b * C ol or Sp ac e G re y‑ sc al e Re fle c‑ ta nc e M un se ll C ol or C IE X Y Z C ol or S pa ce C IE L *a *b * C ol or Sp ac e X Y Z L* a* b* X Y Z L* a* b* X Y Z L* a* b* 8. 67 8 0. 9Y 3. 38 /1 .7 4 10 .3 4 8. 79 2. 02 35 .5 7 5. 2 12 .0 7 4. 79 4 2. 7Y 2. 53 /0 .8 7 5. 5 4. 85 1. 36 26 .2 9 2. 04 5. 6 3. 00 6 2. 5Y 1. 93 /1 .0 1 3. 5 3. 05 0. 78 20 .2 3 2. 39 6. 42 18 .5 39 1. 0Y 4. 80 /2 .0 3 21 .9 4 18 .8 2 4. 5 50 .4 8 5. 71 14 .2 3 5. 86 5 2. 4Y 2. 81 /0 .9 2 6. 75 5. 93 1. 65 29 .2 3 2. 33 6. 15 4. 12 1 3. 7Y 2. 32 /1 .0 2 4. 74 4. 17 1. 11 24 .2 3 1. 95 6. 36 16 .6 93 1. 9Y 4. 59 /1 .7 8 19 .5 7 16 .9 4 4. 18 48 .1 9 4. 64 12 .7 4 14 .3 02 2. 6Y 4. 32 /0 .8 4 16 .2 4 14 .4 5 4. 29 44 .8 7 2 6. 15 4. 75 6 3. 2Y 2. 51 /1 .1 2 5. 49 4. 8 1. 25 26 .1 6 2. 41 7. 24 15 .9 15 1. 1Y 4. 48 /2 .1 6 18 .9 8 16 .1 7 3. 65 47 .2 6. 1 15 .3 7 13 .6 58 2. 3Y 4. 22 /0 .9 0 15 .5 6 13 .8 4. 03 43 .9 5 2. 26 6. 62 9. 68 7 2. 6Y 3. 58 /1 .5 0 11 .3 9. 83 2. 42 37 .5 3 3. 54 10 .6 5 15 .8 93 1. 3Y 4. 48 /2 .0 3 18 .8 3 16 .1 1 3. 73 47 .1 2 5. 69 14 .5 11 .8 2 2. 4Y 3. 95 /0 .8 8 13 .4 8 11 .9 5 3. 47 41 .1 3 2. 22 6. 48 9. 58 3. 4Y 3. 58 /0 .9 4 10 .9 1 9. 68 2. 74 37 .2 7 1. 99 6. 74 19 .5 94 0. 7Y 4. 91 /2 .3 3 23 .4 3 19 .9 1 4. 53 51 .7 4 6. 75 16 .1 6 9. 89 2 2. 4Y 3. 64 /0 .8 8 11 .3 1 10 .0 1 2. 88 37 .8 6 2. 17 6. 36 13 .5 88 3. 7Y 4. 21 /1 .1 3 15 .4 9 13 .7 6 3. 8 43 .8 8 2. 14 8. 34 18 .8 3 1. 1Y 4. 83 /2 .2 5 22 .4 5 19 .1 9 4. 39 50 .9 1 6. 13 15 .8 1 7. 43 2. 4Y 3. 17 /0 .8 6 8. 51 7. 52 2. 14 32 .9 5 2. 14 6. 02 13 .1 77 3. 9Y 4. 15 /1 .1 0 15 13 .3 4 3. 7 43 .2 6 2. 01 8. 12 19 .5 64 0. 6Y 4. 91 /2 .2 2 23 .3 7 19 .9 4 4. 65 51 .7 7 6. 38 15 .3 8 3. 89 6 2. 5Y 2. 25 /0 .9 2 4. 49 3. 94 1. 07 23 .4 7 2. 16 5. 79 7. 47 6 3. 3Y 3. 18 /1 .1 4 8. 59 7. 57 2. 01 33 .0 7 2. 3 7. 86 18 .4 42 1. 0Y 4. 79 /2 .3 7 22 .1 2 18 .8 4 4. 19 50 .5 6. 45 16 .6 2. 68 6 2. 3Y 1. 79 /0 .9 3 3. 14 2. 72 0. 69 18 .8 9 2. 44 6. 32 5. 70 6 3. 2Y 2. 76 /1 .0 6 6. 55 5. 76 1. 54 28 .8 2. 27 7. 05 17 .7 38 1. 8Y 4. 72 /1 .8 0 20 .8 2 18 .0 3 4. 47 49 .5 4 4. 71 12 .8 5 1. 89 3 2. 3Y 1. 40 /0 .7 0 2. 21 1. 91 0. 48 15 .0 2 2. 19 5. 73 9. 00 9 3. 6Y 3. 48 /1 .1 7 10 .3 5 9. 13 2. 44 36 .2 3 2. 34 8. 24 15 .4 1. 4Y 4. 43 /1 .7 4 18 .1 5 15 .6 6 3. 85 46 .5 3 4. 88 12 .4 7 2. 37 5 2. 4Y 1. 65 /0 .7 8 2. 75 2. 4 0. 62 17 .4 4 2. 2 5. 74 6. 56 3 3. 5Y 2. 98 /1 .0 5 7. 53 6. 64 1. 79 30 .9 8 2. 12 7. 13 16 .8 25 2. 6Y 4. 63 /1 .3 1 19 .3 8 17 .0 8 4. 64 48 .3 6 3. 04 9. 53 3. 15 5 2. 5Y 1. 98 /1 .0 5 3. 66 3. 18 0. 82 20 .7 6 2. 46 6. 45 6. 01 5 3. 2Y 2. 84 /1 .1 1 6. 93 6. 09 1. 61 29 .6 3 2. 34 7. 44 17 .1 73 1. 9Y 4. 67 /1 .4 1 19 .9 1 17 .4 2 4. 67 48 .7 9 3. 68 10 .1 10 .1 1 2. 6Y 3. 66 /1 .3 9 11 .7 7 10 .2 6 2. 61 38 .3 3. 45 9. 89 4. 35 3 3. 2Y 2. 39 /0 .7 6 4. 95 4. 38 1. 26 24 .8 9 1. 67 4. 83 17 .8 49 1. 4Y 4. 74 /1 .6 6 20 .9 2 18 .1 6 4. 66 49 .6 8 4. 54 11 .7 2 6. 38 7 2. 3Y 2. 93 /1 .2 4 7. 46 6. 48 1. 66 30 .6 3. 14 8. 36 5. 73 2 1. 6Y 2. 77 /0 .9 9 6. 65 5. 8 1. 58 28 .9 2. 81 6. 62 17 .9 42 1. 4Y 4. 75 /1 .5 7 20 .9 3 18 .2 1 4. 75 49 .7 5 4. 34 11 .1 4 3. 58 9 2. 6Y 2. 13 /1 .6 2 4. 29 3. 66 0. 79 22 .5 3. 68 10 .1 4 6. 20 5 1. 1Y 2. 88 /0 .9 6 7. 2 6. 26 1. 73 30 .0 7 2. 98 6. 45 13 .3 1. 7Y 4. 15 /1 .5 6 15 .6 1 13 .5 3 3. 39 43 .5 5 4. 23 11 .3 6 2. 95 3 2. 9Y 1. 90 /1 .1 8 3. 47 3 0. 73 20 .0 5 2. 74 7. 48 5. 94 5 2. 8Y 2. 82 /1 .0 6 6. 84 6. 01 1. 61 29 .4 3 2. 41 7. 1 12 .1 14 1. 5Y 3. 97 /1 .6 5 14 .3 12 .3 2 2. 98 41 .7 2 4. 62 12 .0 2 2. 53 2 2. 6Y 1. 72 /0 .9 1 2. 95 2. 56 0. 65 18 .1 8 2. 45 6. 36 14 .8 73 2. 3Y 4. 39 /1 .1 6 17 .1 15 .0 8 4. 19 45 .7 5 2. 83 8. 47 13 .6 43 0. 9Y 4. 19 /1 .7 9 16 .2 13 .8 7 3. 31 44 .0 5 5. 34 12 .9 2. 13 4 2. 3Y 1. 53 /0 .7 2 2. 48 2. 15 0. 56 16 .2 7 2. 3 5. 53 13 .5 2 3. 6Y 4. 21 /1 .0 3 15 .4 1 13 .7 3. 87 43 .8 2. 05 7. 61 15 .7 23 1. 6Y 4. 48 /1 .4 0 18 .2 5 15 .9 2 4. 23 46 .8 7 3. 89 10 .0 7 2. 39 6 2. 4Y 1. 66 /0 .8 5 2. 79 2. 43 0. 62 17 .5 8 2. 32 6. 17 10 .9 5 3. 0Y 3. 81 /1 .3 2 12 .6 6 11 .1 2 2. 88 39 .7 8 2. 93 9. 63 17 .6 21 0. 9Y 4. 69 /2 .1 3 20 .9 9 17 .9 2 4. 16 49 .4 6. 09 14 .9 6 3. 51 1 2. 6Y 2. 11 /1 .0 4 4. 07 3. 55 0. 93 22 .1 3 2. 33 6. 45 9. 67 9 3. 3Y 3. 60 /1 .1 0 11 .0 9 9. 8 2. 67 37 .4 8 2. 32 7. 89 Environmental Earth Sciences (2025) 84:85 85   Page 10 of 19 Ta bl e  2   (c on tin ue d) S- 20 21 S- 20 03 S- 19 78 G re y‑ sc al e Re fle c‑ ta nc e M un se ll C ol or C IE X Y Z C ol or S pa ce C IE L *a *b * C ol or Sp ac e G re y‑ sc al e Re fle c‑ ta nc e M un se ll C ol or C IE X Y Z C ol or S pa ce C IE L *a *b * C ol or Sp ac e G re y‑ sc al e Re fle c‑ ta nc e M un se ll C ol or C IE X Y Z C ol or S pa ce C IE L *a *b * C ol or Sp ac e X Y Z L* a* b* X Y Z L* a* b* X Y Z L* a* b* 16 .8 04 0. 1Y 4. 59 /1 .9 0 19 .9 9 17 .0 6 4. 15 48 .3 4 6. 03 13 .2 4 5. 50 5 2. 5Y 2. 71 /1 .1 9 6. 41 5. 59 1. 43 28 .3 4 2. 76 7. 87 7. 48 4 3. 7Y 3. 18 /1 .1 3 8. 6 7. 59 2. 02 33 .1 1 2. 2 7. 78 16 .8 93 2. 3Y 4. 64 /1 .2 3 19 .4 17 .1 4. 74 48 .3 8 3 8. 86 6. 42 3. 5Y 2. 95 /1 .0 6 7. 37 6. 5 1. 75 30 .6 3 2. 13 7. 12 14 .4 56 1. 2Y 4. 31 /1 .3 6 16 .8 3 14 .6 5 3. 89 45 .1 6 3. 94 9. 84 6. 27 3 3. 5Y 2. 91 /1 .0 7 7. 2 6. 35 1. 7 30 .2 8 2. 16 7. 19 13 .3 52 1. 2Y 4. 16 /1 .4 5 15 .6 2 13 .5 4 3. 48 43 .5 7 4. 24 10 .5 1 5. 62 6 3. 4Y 2. 75 /1 .0 0 6. 44 5. 68 1. 55 28 .5 9 2. 05 6. 58 14 .4 19 2. 2Y 4. 31 /1 .4 5 16 .7 8 14 .6 5 3. 8 45 .1 5 3. 72 10 .5 3 9. 48 5 3. 5Y 3. 56 /1 .2 4 10 .9 9. 61 2. 52 37 .1 3 2. 48 8. 82 12 .4 13 2. 0Y 4. 03 /1 .3 1 14 .4 1 12 .5 8 3. 31 42 .1 3 3. 54 9. 57 10 .8 45 3. 4Y 3. 79 /1 .1 1 12 .4 1 10 .9 7 2. 99 39 .5 3 2. 33 8. 11 13 .9 61 2. 0Y 4. 25 /1 .5 1 16 .3 1 14 .2 3. 62 44 .5 2 3. 92 10 .9 9 8. 90 2 3. 1Y 3. 45 /1 .1 7 10 .2 4 9. 02 2. 4 36 .0 2 2. 51 8. 32 13 .1 94 1. 0Y 4. 13 /1 .6 5 15 .5 7 13 .3 8 3. 29 43 .3 4 4. 93 11 .9 1 7. 71 4 3. 0Y 3. 22 /1 .2 7 8. 93 7. 82 2. 01 33 .5 9 2. 81 8. 76 15 .9 65 2. 0Y 4. 51 /1 .6 9 18 .6 9 16 .2 3 4. 05 47 .2 8 4. 34 12 .1 8 5. 82 5 2. 9Y 2. 79 /1 .1 7 6. 73 5. 89 1. 53 29 .1 4 2. 57 7. 82 16 .7 57 1. 5Y 4. 61 /1 .2 4 19 .3 3 16 .9 4 4. 69 48 .1 9 3. 52 8. 89 5. 59 8 3. 7Y 2. 74 /0 .9 8 6. 4 5. 66 1. 55 28 .5 3 1. 9 6. 47 Environmental Earth Sciences (2025) 84:85 Page 11 of 19  85 a matrix-supported texture (packstones), with occasional clastic-supported zones (wackstones). Patches of recrystallization to dolomite, typical in the Urgonian limestones, were not observed. This fact seems to be extrapolated to the Santullán massif based on the enor‑ mous purity of these limestones, whose chemical analyses showed MgO contents lower than 0.3% in all cases. Biological colonisation Biological colonisation in the 2003 and 1978 quarry fronts was macroscopically and microscopically assessed and com‑ pared with the fresh massif surface (S-2021). Exposure to environmental conditions causes the rock surface to develop dark colorations (Figs. 3C, 4), likely due to the formation of biological patinas. BSE/EDS-SEM observations reveal extensive microbial colonisation on these darkened surfaces, particularly involving algal and fungal cells. These fungal and algal cells are found on the surface and within internal rock fissures, often aligned paral‑ lel to the surface. This endolithic colonisation is primarily found associated with the inter and intracrystalline porosity of the limestone. As a result, clusters of algal cells (Fig. 9C- 3) and fungal hyphae (Fig. 9B-3) are frequently detected beneath the limestone's surface, forming an extensive endo‑ lithic network within the porous spaces between the calcite crystals. Fungal endolithic mycelia can extend from the sur‑ face to more than 100 µm beneath it. In some areas, extensive euendolithic colonisation was observed (Figs. 9, 10). These microorganisms were identi‑ fied as algal cells (Fig. 10E–G) based on their morphological characteristics observed using the “SEM-BSE technique.” They create a homogeneous network of internal cavities beneath the surface by forming micropits that contain indi‑ vidual algal cells 10–20 µm in diameter (Fig. 10). Endolithic colonisation in the 1978 quarry front was more extensive than in the 2003 front, with an evident increase in the deepness of the colonisation and, consequently, the thick‑ ness of the bioaltered layer (Fig. 10E–G). As Fig. 9 shows, the depth of penetration of the microorganisms increases with time, being between 40 and 50% higher in the samples from the oldest front (1978) compared to the front exposed in 2003, with average depths reaching 50 µm and 100 µm, respectively. Cyanobacteria (white arrows in Fig. 10F, G) and heterotrophic bacteria (red arrow in Fig. 10G) are also detected near the euendolithic algal cells. As shown in Fig. 11, the distribution of microbial cells is influenced by the texture of the substrate, with a higher concentration in the sparitic facies, where the crystals are coarse. In these areas, the microorganisms do not rely on the boundaries between crystals; instead, they create poros‑ ity within the crystals themselves, forming intracrystalline porosity. Discussion Mining operations produce a negative visual effect that alters the landscape's character. The causes of these altera‑ tions are diverse and involve many subjective factors, such as individual perception and aesthetic taste (Byizigiro et al. 2015; Manna and Maiti 2014). While many of those adverse effects have been partially abated with the application of new technologies, landscape alteration represents a primary ele‑ ment of the overall environmental impact, especially when those modifications are visible from major residential areas Table 3   Percentage of reflectance as a function of wavelength for the samples of the three analyzed fronts Reflectance (%) (nm) S-2021 S-2003 S-1978 Wavelength (nm) 400 8.32 3.50 4.88 410 8.73 3.65 5.06 420 9.23 3.88 5.31 430 9.83 4.14 5.60 440 10.42 4.31 5.79 450 10.85 4.40 5.93 460 11.14 4.47 6.04 470 11.36 4.53 6.17 480 11.68 4.61 6.32 490 12.04 4.74 6.51 500 12.51 4.88 6.71 510 13.01 5.03 6.93 520 13.52 5.18 7.15 530 14.02 5.33 7.37 540 14.57 5.48 7.62 550 15.14 5.64 7.83 560 15.73 5.80 8.04 570 16.26 5.93 8.21 580 16.71 6.03 8.33 590 17.03 6.11 8.40 600 17.28 6.15 8.46 610 17.48 6.20 8.50 620 17.67 6.25 8.56 630 17.84 6.29 8.60 640 18.02 6.34 8.67 650 18.21 6.40 8.75 660 18.40 6.45 8.82 670 18.60 6.49 8.89 680 18.85 6.57 9.03 690 19.06 6.71 9.26 700 19.32 6.89 9.59 Environmental Earth Sciences (2025) 84:85 85   Page 12 of 19 or tourist sites (Mavrommatis and Menegaki 2017; Alphan 2017). Most often, there is a mismatch or excessive contrast between the visual elements of the operation and those of the surroundings, a contrast that can come from several ele‑ ments, but color plays a fundamental role. Several legislations worldwide have included landscape and visual impact assessments as part of the Environmental Impact Assessment linked to mining activities (Tudor 2014). In mountain quarries, visual impact mitigation strategies by installation of shielding and/or re-vegetation are often only partially feasible due to the high intervisibility of the height and steep vertical reliefs. In these cases, the study of the color variations proves significant because it allows us to anticipate what the quarry might be like, which can help define rehabilitation programs more effectively. Fig. 6   Reflectance (in %) versus wavelengths of the visible spec‑ trum (400–700 nm) Fig. 7   Comparison of XRD diffractograms for the differ‑ ent sample quarry fronts 2022 (black), 2003 (red), and 1978 (blue) Table 4   Comparison of the total color difference between samples from the three different fronts ΔEab* S-1978 S-2003 S-2021 S-1978 – 3.42 14.43 S-2003 3.42 – 20.64 S-2021 14.43 20.64 – Environmental Earth Sciences (2025) 84:85 Page 13 of 19  85 The Santullán quarry's open fronts are darker than the surrounding natural massif. In many quarries, blackening is caused by the embedding of air pollutant particles origi‑ nating from different sources, such as suspended particles (dust, ashes) and organic pollutants, mostly from combustion reactions associated with industrial activity (e.g. Del Monte et al. 1984; Nord and Tronner 1991; Whalley et al. 1992; Saiz Jimenez 1993). Here, the presence of sulfur (Table 5) and some other metals observed in the XRF analysis of the S-1978 sample, taken in the oldest quarry front, can be related to the pollution from traffic and other industrial activities since this front occupies the central quarry shaft close to the crushing plant. Commonly, the preferential dry deposition of sulfur dioxide, which is an abundant impurity in fossil fuels, onto the moist surface of calcareous rocks stone, followed by the dissolution of calcite, can lead to the precipitation of gypsum crusts (Schiavon 1992; Vergès-Belmin 1994). However, the low concentrations of chemical compounds associated with pollution, the absence of gypsum crusts, and the observations made by the analytical methods used in this work suggest that other possible causes are respon‑ sible for the darkening of the Santullán quarry faces. Color changes of a rock surface exposed to meteoric conditions are usually due to precipitation of patinas (Hess et al. 2008; Gonzalez-Gomez et al. 2018), alteration reactions of chromophore elements, biological activity on the rock surfaces (Prieto et al. 2005; Monzó and García del Cura 1999; Prieto et al. 2005) or a combination of these pro‑ cesses (Benavente et al. 2003; De los Rios et al. 2009). The influence of the segregation of iron and manga‑ nese oxyhydroxides due to weathering processes has been evaluated. Nevertheless, XRF geochemical rock analysis carried out on more than 60 samples from different points of the Santullán quarry showed mean concentrations of iron oxide lower than 0.16% and manganese oxide of 0.04%. In addition, the spectrometric analyses would also have revealed changes in the hue component of color if chromophore elements were abundant. The observations showed that the band structures corresponding to those specific elements remained constant without modifying visible bands. The high purity of the limestones and the low concentrations of chromophore elements discard the possibility of a preponderant role of manganese and iron oxides in the color changes. Another common blackening phenomenon in porous limestones is the precipitation of calcium oxalate patinas (Török 2002). This oxalate type is less soluble than the original calcite mineral and can form a crust on the rock surface (Eq. 1). Table 5   The concentration of major and minor elements analysed by XRF (expressed as percentage w/w) (%) S-1978 S-2003 S-Fresh S 0.1785 (Avg. ± 0.0466) 0.0982 (Avg. ± 0.0567) 0.1424 (Avg. ± 0.039) K 0.2269 (Avg. ± 0.0601) 0.074 (Avg. ± 0.0175) 0.3301 (Avg. ± 0.0576) Ca 42.6512 (Avg. ± 2.2944) 34.569 (Avg. ± 4,6578) 43.5327 (Avg. ± 2.2793) Ti 0.0388 (Avg. ± 0.0087) 0.0135 (Avg. ± 0.004) 0.0588 (Avg. ± 0.0157) Cr 0.005 (Avg. ± 0.0100) – – Mn 0.0159 (Avg. ± 0.0050) 0.011 (Avg. ± 0.0017) 0.0149 (Avg. ± 0.0054) Fe 0.3128 (Avg. ± 0.3128) 0.1286 (Avg. ± 0.1286) 0.3462 Ni 0.0023 (Avg. ± 0.0019) – 0.0022 Zn 0.0046 (Avg. ± 0.0007) 0.0033 (Avg. ± 0.0021) 0.001 (Avg. ± 0.0012) As 0.0003 (Avg. ± 0.0002) 0.0001 (Avg. ± 0.0002) 0.0000 (Avg. ± 0.0001) Se 0.0002 (Avg. ± 0.0001) 0.0001 (Avg. ± 0.0001) 0.0000 (Avg. ± 0.0001) Rb 0.0008 (Avg. ± 0.0002) – 0.0012 (Avg. ± 0.0003) Sr 0.0208 (Avg. ± 0.0016) 0.0139 (Avg. ± 0.0032) 0.0236 (Avg. ± 0.0025) Zr 0.001 (Avg. ± 0.0002) – 0.0013 (Avg. ± 0.0004) Nb 0.0004 (Avg. ± 0.0003) 0.0002 (Avg. ± 0.0003) 0.0004 (Avg. ± 0.0003) Mo 0.0001 (Avg. ± 0.0003) – – Ag 0.0009 (Avg. ± 0.0018) – 0.0008 (Avg. ± 0.0017) Cd 0.0007 (Avg. ± 0.0009) 0.0004 (Avg. ± 0.0005) 0.0005 (Avg. ± 0.0004) Sn 0.006 (Avg. ± 0.003) – 0.0059 (Avg. ± 0.0031) Sb 0.0022 (Avg. ± 0.0011) 0.0007 (Avg. ± 0.0015) 0.0018 (Avg. ± 0.0023) Ba 0.0102 (Avg. ± 0.0053) 0.0027 (Avg. ± 0.0054) 0.0087 (Avg. ± 0.0076) Ta – 0.0009 (Avg. ± 0.0011) 0.0008 (Avg. ± 0.001) Hg 0.0009 (Avg. ± 0.0002) 0.0003 (Avg. ± 0.0003) 0.0005 (Avg. ± 0.0004) Environmental Earth Sciences (2025) 84:85 85   Page 14 of 19 Ca-oxalates in the form of whewellite (CaC2O4 H2O) and weddellite (CaC2O4 2H2O) have been documented both in historical monuments and in natural limestone and marble outcrops (Del Monte et  al. 1987; Watch‑ man 1991; Prieto et al. 2005). Ca-oxalate is ubiquitously associated with the colonisation of lichen-forming fungi and the establishment of the lichen thallus on the rock surface (Gaad et al. 2014; Pinzari et al. 2010; Burford et al. 2006). These organisms transform calcium carbon‑ ate into calcium oxalates as a critical metabolite product (Chen et al. 2000). The lichen-induced precipitation of Ca-oxalate requires decades to centuries (Del Monte et al. 1987) and pristine natural environments, as lichens are very sensitive to atmospheric conditions. The relatively short time (> 30 years) since the opening of the quarry fronts, together with the presence of dust in suspension and fuel emissions, seem responsible for the limited devel‑ opment of epilithic lichens and, thus, Ca-oxalate patinas. Yet, some crystal morphologies observed using the SEM resemble Ca-oxalate crystals, indicating that it is also (1)Ca 2+ + C 2 O 2− 4 + 2H 2 O → Ca ( C 2 O 4 ) ⋅ xH 2 O(s) ↓ possible that Ca-oxalate was replaced by calcite (Verrec‑ chia et al. 1993). Despite the scarcity of lichens, intense microbial col‑ onisation has been demonstrated on the surfaces of the fronts opened in 1978 and 2021, including primary euen‑ dolithic algal cells and cyanobacteria and heterotrophic bacterial colonies nearby. Phototrophic microorganisms are the first colonizers of rock in outdoor environments, commonly forming greenish-blackish patinas and con‑ sequently changing the color of colonized rock surface (Gorbushina 2007; Hauer et al. 2015). These lithobiontic communities dominated by phototrophic microorganisms include commonly epilithic and endolithic forms (Hoppert et al. 2004; De los Ríos and Souza-Egipsy 2022). Euendo‑ lithic microorganisms, such as those observed in Santullan exposed rocks, cause significant alterations in carbonate rocks by actively penetrating them (Golubic et al. 1981). Consequently, the observed euendolithic microorganisms may be responsible not only for changes in the appear‑ ance of the exposed rock but also for significantly modify‑ ing the texture and porosity of the surface layer (Figs. 9, 10). Microbial colonisation could play a pivotal role in Fig. 8   Photomicrographs of the most characteristic facies of the bio‑ sparite limestones (A, B) and the bioclastic micrites (C, D). A Bio‑ sparite clast-supported texture; B mosaic of sub-euhedral sparite crystals filling a fissure. Fragments of bryozoans (C) and foraminifera (D) embedded in the micritic matrix Environmental Earth Sciences (2025) 84:85 Page 15 of 19  85 weathering the rock surface in the Santullan massif. The involvement of photosynthetic microorganisms and lichens in bioalteration processes is particularly significant on limestone surfaces (Ascaso et al. 1982; De los Ríos et al. 2009). Indeed, the activity of endolithic microorganisms induces chemical processes that can contribute to the dis‑ solution of carbonate rock minerals and the disaggrega‑ tion of the rock surface (Sohrabi et al. 2017). This process likely involves the production of extracellular polymeric substances and the excretion of organic acids (Banfield et al. 1999b, a, Chen et al. 2000; De los Ríos and Souza Egipsy 2022; Nir et al. 2022). All these changes have altered the originally non-porous limestone surface in the Santullán area, creating porosity that facilitates microbial colonisation unrelated to the properties of the original material. These changes could favor more complex colo‑ nisation patterns over time, including the establishment of lichens on the exposed rocks following the primary succession process (Hoppert et al. 2004; Garrido-Benavent et al. 2021). All the above highlights microorganisms' significant role in coloring rock surfaces, whether they are free-living or form symbiotic associations such as lichens. This influence is particularly evident in the formation of patinas and crusts in areas where conditions are unfavorable for other forms of life. The study of their biological colonisation can be monitored and even accelerated using catalysts of biological activity (Leifeld et al. 2001; Prieto et al. 2002, 2004; Moldes et al. 2006; Paradelo et al. 2006) to reduce the time needed to reach conditions of lower chromatic contrast. The red-colored patina at the sample S-1978 surface has been ascribed to the presence of both iron oxy- hydroxide and carotenoid pigments. However, this last cannot be ensured entirely because of the low signal/ noise ratio and high fluorescence effects. Albeit a 785 nm excitation source for Raman spectroscopic analysis shows Fig. 9   BSE/EDS-SEM images comparing at different scales the front surfaces from samples from fresh rock (A), 2003 exposed front (B), and 1978 exposed front (C). Note that associated with this algal (and locally, fungi) endolithic colonisation there is an intense alteration of the internal structure of the limestone, especially in areas with calcite cement Environmental Earth Sciences (2025) 84:85 85   Page 16 of 19 better performance in geomicrobiological systems, dis‑ criminating between different pigments and carotenoids, the 514.5 nm wavelength is a better choice where a low concentration of organic material is a limiting factor as is the case (Vitek et  al. 2013). The presence of other non-carotenoid pigments, such as scytonemin and gloe‑ ocapsin, is also feasible. Still, the resonance-enhanced carotenoid signal is ubiquitous and much stronger, hiding the signal of the other pigments (Němečková et al. 2021). Fig. 10   Development of endolithic biofilms in Santullan limestones over 40  years of exposure. BSE-SEM images of cross sections per‑ pendicular to the surface from a 2003 quarry front sample (A, C, E, G) and a 1978 quarry front sample (B, D, F). E, F, G are images of the area occupied by euendolithic algal cells obtained with the “SEM-BSE technique”; the red arrow notes heterotrophic bacteria and the white arrow cyanobacteria. Note the irregular but clear inter‑ face (bioalteration front) between the unweathered rock and the sur‑ face affected by biogenic processes and how it increases progressively deep in the oldest sample. The upper layer is dominated by algal cells within small endolithic cavities created by active substrate dissolution Environmental Earth Sciences (2025) 84:85 Page 17 of 19  85 Conclusions Color changes between the fresh surface of the massif and those samples exposed to meteoric conditions for several decades at the quarry faces are visible to the naked eye. The color coordinates of the fresh surface of the massif indicate a predominance of greyish colors, with a very slight contribu‑ tion of yellow and red (positive quadrants of coordinates a* and b*). A comparison of the values of the main parameters analyzed shows that the effect of the exposure of these sur‑ faces generates an apparent decrease in the values of all the parameters, close to 50% of luminosity, a*, b*, reflectance, and chroma (C*ab). Only the hue (hab) is similar in the three cases, remaining in grey tones. It is noteworthy that the most abrupt variations occur between the fresh cut sample (S-2021) and the one from 2003 (S-2003) and not with the sample that has been exposed to environmental conditions for the longest time (S-1978), indicating that the effects on color change are not progres‑ sive or linear, i.e., the most critical color change occurs dur‑ ing a certain number of years and, after that period, there is no longer a direct relationship with the color variation. Mineralogical, geochemical, and SEM observations showed that color change was due mainly to changes in the extension of biological colonisation and not to chemi‑ cal reactions that may have altered the oxidation state of the chromophore elements present in the rock. In any case, there is no change in the hue because the band structures of the chromophore compounds of the stone remain constant, without any changes in the allowed and forbidden transitions in the visible band. The interaction of the physico-chemical phenomena of the exposed rock (oxidations, dissolution/ precipitation processes, etc.) with the biological colonizing activity is undoubtedly responsible for the variations in color on the surface of the fronts. It has been proved that the significant surface changes detected are primarily related to colonisation by microorgan‑ isms and associated bioweathering processes. The limestone surface is predominantly colonized by endolithic phototro‑ phic microorganisms that penetrate the rock substratum independently of existing pores or fissures. These organisms create a network of ducts and cavities by actively dissolving the substrate. Biological colonisation progresses over time, marked by an increase in the number of microbial cells, the extent of surface bioalteration, and the depth of penetration into the rock substrate. Acknowledgements  Project Nº supported this research. 2943 INREC‑ MINOR Centro Nacional Instituto Geológico y Minero de España (CSIC-IGME). The authors are grateful for the collaboration of Can‑ teras de Santullán, S.A., which has made its facilities, means, and per‑ sonnel available to the project, and a special mention to its technical director, Pedro de Andrés, the mining engineer Guillermo Careaga and consultant Pedro Jiménez (CRS). Studies with the “SEM-BSE tech‑ nique” were financed by the program TOP-HERITAGE S2018/NMT- 4372 (Comunidad de Madrid, FSE, FEDER). The authors are also grateful for the help provided by Luís Galán in spectrophotometric studies and to the staff of the IGME laboratory in Tres Cantos, Elena Fernández, Ana Gimeno, and Jesús Reyes. Author contributions  All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by M.I., P.D., And X.A. The first draft of the manuscript was written by M.I., J.F., A.R. and C.P. and revised by M.L.G.L., E.C.. All authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Funding  Open access funding provided by CSIRO Library Services. Data availability  No datasets were generated or analysed during the current study. Declarations  Conflict of interest  The authors declare no competing interests. Open Access  This article is licensed under a Creative Commons Attri‑ bution 4.0 International License, which permits use, sharing, adapta‑ tion, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. Fig. 11   BSE-SEM images of 1978 front sample. Note the preferential accumulation of microorganisms in micritic or microsparitic zones with a lower presence of colonisation in coarser sparitic facies. Right) Intracrystalline porosity gener‑ ated by endolithic cavities http://creativecommons.org/licenses/by/4.0/ Environmental Earth Sciences (2025) 84:85 85   Page 18 of 19 References Alphan H (2017) Assessing visibility of marble quarries from a scenic coastal Road. 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View publication stats https://doi.org/10.1016/j.still.2005.12.007 https://doi.org/10.1016/j.still.2005.12.007 https://doi.org/10.1007/s00254-002-0537-5 https://doi.org/10.1016/j.catena.2004.03.001 https://www.gov.uk/government/publications/landscape-character-assessments-identifying-and-describing-landscapetypes https://www.gov.uk/government/publications/landscape-character-assessments-identifying-and-describing-landscapetypes https://www.gov.uk/government/publications/landscape-character-assessments-identifying-and-describing-landscapetypes https://doi.org/10.1080/01490451.2012.697976 https://doi.org/10.1080/01490451.2012.697976 https://www.researchgate.net/publication/379547817 Chromatic evolution, chemical changes, and biological colonisation in the quarry fronts of the Santullán limestone massif (Cantabria, Spain): implication for the mitigation of visual impact in mountain quarrying Abstract Introduction Geology and natural environment Methodology Petrological characterization Chemical analysis by X-ray fluorescence Color determination by UV-Vis spectrophotometry Scanning electron microscope and X-ray diffraction analysis Micro-Raman spectroscopy analysis Results Mineralogical characterization of sample patinas Geochemistry of rock surfaces Chemical analysis by X-ray fluorescence Petrological characterisation Biological colonisation Discussion Conclusions Acknowledgements References