The Optical and Spectroscopic Properties of Fuchsite, Spodumene, and Lepidolite from Northern Scandinavia (Kautokeino, Kaustinen, Kolmozero)

Li-Ce-Ta (LCT) pegmatites containing lithium mineralization in the form of spodumene and lepidolite, as well as fuchsite, from the regions of northern Scandinavia (N Norway, N Finland, N Russia) were studied. Detailed analyses of the chemical compositions of these minerals were carried out, involving scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy with attenuated total reflectance (ATR), and X-ray photoelectron spectroscopy (XPS) studies. Their crystal structures were confirmed with the X-ray diffraction technique. Studies involving microscopy were also carried out, indicating the optical features of these minerals. Based on the analyses carried out in the studied rocks, the characteristics of these minerals were determined, as well as the crystallization conditions. This research indicates that the N Scandinavian area is prospective and may lead to further discoveries of this type of pegmatite in the studied region.


Introduction
In northern Scandinavia, pegmatite veins containing rare lithium and schists with chromium minerals are found in the regions of northern Norway [1], Finland [2], and the Kola Peninsula in Russia [3], among rocks constituting the cratonic basement of the Northern Fennoscandia [4]. These rocks contain minerals such as mica (lepidolite, fuchsite, muscovite) and pyroxene (spodumene), which co-occur with quartz, plagioclase, orthoclase, and several ore minerals: oxides (e.g., columbite, tantalite, cassiterite, sillenite, clarkeite) and sulfides (pyrite, chalcopyrite). Their thickness reaches several meters, and they cut through their metamorphic host rocks [5]. The previous study of these rocks was mainly concerned with analyses for the needs of economic geology [6]. The purpose of this article is a detailed analysis of the mineralogy of these rocks and a discussion of the crystalline structure characteristics of spodumene, lepidolite, and fuchsite.

Host Rock Petrology
The examined lithologies are located in the Kolmozero-Voronya Greenstone Belt, Pohjanmaa Schist Belt (Kaustinen Pegmatites), and Kautokeino Greenstone Belt. The LCT pegmatites from the Kolmozero area are located in the Kolmozero-Voronya Greenstone Belt, separating the Murmansk block from the Kola block, composed of mixed metasediments and metavolcanites. These formations are intersected by numerous intrusions of alkaline and acidic rocks. The discussed LCT pegmatites intersect the alkaline rocks of the Patchemvarek anorthosite intrusion. This intrusion is located on the border of the Kolmozero block with the plagiogranites of the Murmansk block [53]. These rocks are in direct contact with biotite gneisses and amphibolites of the Kolmozero-Voronya Belt. There are fine-grained tourmaline-muscovite granites with pegmatite apophyses rich in tourmaline, garnet, and apatite. The studies of Kudrashov et al. [54] indicated that these are pegmatites of hydrothermal-metasomatic origin [55,56]. The Kaustinen pegmatite province is located in Western Finland. It is situated among supracrustal rocks belonging to the Pohjanmaa Schist Belt [57,58]. It is surrounded by the Vaasa granitoid complex to the west and Central Finland granitoides to the east [6]. The Pohjanmaa Schist Belt is composed of micaceous schists and gneisses, along with metavolcanic rocks. These rocks were metamorphosed under the amphibolite facies of 1.89-1.88 Ga [59]. The lithium-rich pegmatites from the Kaustinen province belong to the albite spodumene type according to the classification ofČerny and Ercit [55]. They were formed during the metamorphism of the rocks of the Pohjanmaa belt. The pegmatites form a complex of veins cutting the rocks of the Pohjanmaa Käpyaho belt and others [60][61][62][63].
In the region of the Palaeoproterozoic Kautokeino Greenstone Belt, where muscovitefuchsite and quartz-orthoclase schists are located between the gneissic Ráiseatnu Complex (1868-1828 Ma) to the west and the metaplutonic Jergul Complex to the east (tonalitetrondhjemite-granodiorite-granite plutonic rocks formed between 2975 and 2776 Ma). In the Kautokeino Greenstone Belt, metasedimentary-metavolcanic rocks are present, with numerous mafic intrusions [27]. The Masi Formation in the Archean basement is formed of a quartz-feldspar conglomerate with muscovite interbedding and ore mineralization composed of iron and copper sulfides (pyrite, chalcopyrite). It is intersected by the mafic sills of the Haaskalehto formation (2220 Ma age). [64] Among these formations are the discussed fuchsite-rich rocks, which may have formed as an alteration product of detrital chromite grains [65].

Kautokeino
The paleoproterozoic metamorphic formations classified as the Alta-Kautokeino Greenstone Belt are exposed in the Kautokeino region. Among these formations, there are mica schists [66] containing fuchsite (Figure 2A). This rock is an intense green-pink, characterized by layering resulting from a gneissic, streaky texture. The rock has a grano-lepidoblastic texture and is also characterized by a glomeroblastic, locally diablastic texture. Under an optical microscope, large quartz crystals are visible, forming irregular, hooked aggregates in contact with each other. Opaque minerals, such as pyrite and chalcopyrite, are visible between the muscovite and fuchsite. Close to the quartz crystals, microcline and Na-rich plagioclase are also present, forming leucocratic zones. In the interstices of plagioclase and microcline, small crystals of epidote are encountered. In addition to these zones are areas richer in femic minerals. They are represented by aggregates of biotite, which co-occur with fuchsite to form a streaky structure in the rock. These minerals form aggregates, resulting in interlaced streaks in the discussed rock. Opaque minerals can be observed, and zircon and apatite are woven into the biotite flakes. The detailed results of the phase studies in the micro-area are discussed below.

Kaustinen
In the Kaustinen area, pegmatites with a silicon-gray color, coarse crystalline structure, and compact, disordered texture are exposed among the gneisses. Their age was determined to be 1.79 Ga (U-Pb method) [67]. Under an optical microscope, the quartz crystals form large grains in contact with each other and closely interlocking. The quartz in the studied rock has wavy extinction. Alongside these are large orthoclase crystals adjacent to the quartz ( Figure 2B). They are accompanied by much smaller tabular grains of Na-rich plagioclase, often between the orthoclase and quartz. Femic minerals are represented by muscovite forming large clusters of flakes, in the background of which fine zircon crystals are visible. Muscovite crystals are near the pyroxene. Biotite is also visible in the form of small flakes, usually between large pyroxene crystals. The pyroxenes in the discussed rock form large crystals, reaching several centimeters in size. They are represented by spodumene (and hypersthene). The spodumene forms compact crystals with jagged boundaries in which quartz and muscovite are visible. The hypersthene is anhedral. Opaque minerals (columbite-tantalite, sillenite) are visible in the form of small

Kaustinen
In the Kaustinen area, pegmatites with a silicon-gray color, coarse crystalline structure, and compact, disordered texture are exposed among the gneisses. Their age was determined to be 1.79 Ga (U-Pb method) [67]. Under an optical microscope, the quartz crystals form large grains in contact with each other and closely interlocking. The quartz in the studied rock has wavy extinction. Alongside these are large orthoclase crystals adjacent to the quartz ( Figure 2B). They are accompanied by much smaller tabular grains of Na-rich plagioclase, often between the orthoclase and quartz. Femic minerals are represented by muscovite forming large clusters of flakes, in the background of which fine zircon crystals are visible. Muscovite crystals are near the pyroxene. Biotite is also visible in the form of small flakes, usually between large pyroxene crystals. The pyroxenes in the discussed rock form large crystals, reaching several centimeters in size. They are represented by spodumene (and hypersthene). The spodumene forms compact crystals with jagged boundaries in which quartz and muscovite are visible. The hypersthene is anhedral. Opaque minerals (columbite-tantalite, sillenite) are visible in the form of small crystals close to the quartz, sometimes also forming solid inclusions, accompanying zircon. The detailed results of the micro-area phase studies are discussed below.

Kolmozero
In the area of the Kola Peninsula between the Kola and Murmansk blocks is the Archean Kolmozero-Voronya Greenstone Belt. Adjacent to the LCT pegmatites are Archean gabbroanorthosites and granitic rocks. The analyzed pegmatites are dated to 1.90-1.86 Ga [68]. The pegmatites containing spodumene and lepidolite are cream-gray-colored rocks with a coarse crystalline texture and a compact, disorderly texture ( Figure 2C). In thin sections, there are large crystals of quartz interlocking with each other. The quartz forms clumped aggregates in the space between the other phases. Alongside these minerals are visible crystals of Na-rich plagioclase. In the described rock, orthoclase, usually reaching a considerable size, is also visible near the other leucocratic minerals. Among the potassium feldspars, microcline usually forms small crystals. Alongside these minerals, flakes of biotite and muscovite can be identified, interspersed among the quartz and plagioclase. Biotite is much less abundant than muscovite, which predominates. In the pegmatites with lepidolite, this mineral accompanies muscovite, forming deformed flake aggregates of varying sizes. Large crystals of spodumene, reaching several centimeters in length, are visible alongside these minerals. They are surrounded by biotite, lepidolite, and plagioclase. In addition, small crystals of opaque minerals are visible near muscovite flakes occurring in interstices of quartz and feldspar. Zircon crystals are also visible within mica flakes. Accessory apatite forms small crystals co-occurring with femic minerals.

SEM-EDS Analyses
In the case of the Kautokeino rocks, the examined trioctahedral mica can mainly be classified as annite and siderophyllite [69][70][71] (Figure 3). These micas co-occur with fuchsite-forming overgrowths (Table A1). and plagioclase. In addition, small crystals of opaque minerals are visible near muscov flakes occurring in interstices of quartz and feldspar. Zircon crystals are also visible with mica flakes. Accessory apatite forms small crystals co-occurring with femic minerals.

SEM-EDS Analyses
In the case of the Kautokeino rocks, the examined trioctahedral mica can mainly classified as annite and siderophyllite [69][70][71] (Figure 3). These micas co-occur with fuc site-forming overgrowths (Table A1).  Dioctahedral micas are represented by muscovite with fuchsite and lepidolite (Table A1). Muscovite usually shows a low Na + content (up to 5 wt.%). In the rocks from Kautokeino, in addition to muscovite, it was found that all the chromic micas examined were fuchsites. Some of the examined chromium micas have a composition characteristic of paragonite ( Figure 4). In addition, an admixture of clinozoisite and epidote (mainly in the Kaustinen pegmatites, Table A1) was found in the discussed rocks. Dioctahedral micas are represented by muscovite with fuchsite and lepidolite (Table  A1). Muscovite usually shows a low Na + content (up to 5 wt. %). In the rocks from Kautokeino, in addition to muscovite, it was found that all the chromic micas examined were fuchsites. Some of the examined chromium micas have a composition characteristic of paragonite ( Figure 4). In addition, an admixture of clinozoisite and epidote (mainly in the Kaustinen pegmatites, Table A1) was found in the discussed rocks.  [72,73], modified by the authors). The element content is expressed in wt. %.
The examined pyroxenes are mainly represented by spodumene, with an Na content of up to 5 wt. %. In the examined samples, spodumene dominates, while admixtures of jade particles occur in small amounts (Table A2). Hypersthene was also found in the latter.
The accompanying leucocratic minerals are represented by quartz, usually with an admixture of up to 4% of aluminum oxide. The plagioclase is represented by albite with a small admixture of oligoclase (4%), as well as andesine (6%) and labradorite (6%). The labradorite is an admixture found mainly in the pegmatites from Kaustinen. Accessory minerals are represented by zircon and apatite. Zircon crystals are mainly found in close association with muscovite flakes. Phosphates are represented mainly by a variety of hydroxyapatites, with approximately 3% carboxy apatite and 2% fluoroapatite.
The opaque minerals in the investigated rocks are represented by multiple phases. In the case of the schists from Kautokeino, the opaque phases include cassiterite and pyrite. In the pegmatite from Kaustinen, the opaque phases include magnetite and ilmenite, accompanied by titanite. Trace or minor cassiterite was also found, as well as galena, sphalerite, and chalcopyrite, which, together with barite, form disseminations. Columbite and Figure 4. Type of dioctahedral micas examined in the discussed rocks (based on [72,73], modified by the authors). The element content is expressed in wt.%.
The examined pyroxenes are mainly represented by spodumene, with an Na content of up to 5 wt.%. In the examined samples, spodumene dominates, while admixtures of jade particles occur in small amounts (Table A2). Hypersthene was also found in the latter.
The accompanying leucocratic minerals are represented by quartz, usually with an admixture of up to 4% of aluminum oxide. The plagioclase is represented by albite with a small admixture of oligoclase (4%), as well as andesine (6%) and labradorite (6%). The labradorite is an admixture found mainly in the pegmatites from Kaustinen. Accessory minerals are represented by zircon and apatite. Zircon crystals are mainly found in close association with muscovite flakes. Phosphates are represented mainly by a variety of hydroxyapatites, with approximately 3% carboxy apatite and 2% fluoroapatite.
The opaque minerals in the investigated rocks are represented by multiple phases. In the case of the schists from Kautokeino, the opaque phases include cassiterite and pyrite. In the pegmatite from Kaustinen, the opaque phases include magnetite and ilmenite, accompanied by titanite. Trace or minor cassiterite was also found, as well as galena, sphalerite, and chalcopyrite, which, together with barite, form disseminations. Columbite and tantalite were also found, although in smaller amounts relative to the Kolmozero pegmatite.

Optical Properties of the Discussed Minerals
Spodumene forms large xenomorphic crystals, with sizes reaching several cm. This mineral usually has a light green color. Sometimes, it resembles plagioclase, which, when undergoing sericitization, also has a slight gray-green tint. In the microscopic image, it sometimes forms a diablastic texture according to the (100) miller index. It is usually found near micas represented by muscovite, lepidolite, and, less often, biotite ( Figure 5). The schist is highly visible. Small admixtures of Fe-oxides can be seen along the schistosity of the rock. The straw color on the thin section has a clear, positive relief, with darkening extinction.

Optical Properties of the Discussed Minerals
Spodumene forms large xenomorphic crystals, with sizes reaching several cm. This mineral usually has a light green color. Sometimes, it resembles plagioclase, which, when undergoing sericitization, also has a slight gray-green tint. In the microscopic image, it sometimes forms a diablastic texture according to the (100) miller index. It is usually found near micas represented by muscovite, lepidolite, and, less often, biotite ( Figure 5). The schist is highly visible. Small admixtures of Fe-oxides can be seen along the schistosity of the rock. The straw color on the thin section has a clear, positive relief, with darkening extinction. Lepidolite forms large lamellar aggregates, usually colored pearly pink. Macroscopically, this mineral forms flakes reaching up to 1cm in size. It is usually quite visible in the rock due to its coloration and luster. In the microscopic image, it forms numerous adhesions of varying sizes. It is present with spodumene, near plagioclase and quartz. Between the mica flakes, rutile be observed. In the thin section, it is colorless, with a faint, negative relief. Under polarized light, it shows second-order interference colors, optically resembling biotite ( Figure 6). Our microscopic observations of lepidolite showed some deformation of its lamellae due to dynamic processes.  Lepidolite forms large lamellar aggregates, usually colored pearly pink. Macroscopically, this mineral forms flakes reaching up to 1 cm in size. It is usually quite visible in the rock due to its coloration and luster. In the microscopic image, it forms numerous adhesions of varying sizes. It is present with spodumene, near plagioclase and quartz. Between the mica flakes, rutile be observed. In the thin section, it is colorless, with a faint, negative relief. Under polarized light, it shows second-order interference colors, optically resembling biotite ( Figure 6). Our microscopic observations of lepidolite showed some deformation of its lamellae due to dynamic processes. tite.

Optical Properties of the Discussed Minerals
Spodumene forms large xenomorphic crystals, with sizes reaching several cm. This mineral usually has a light green color. Sometimes, it resembles plagioclase, which, when undergoing sericitization, also has a slight gray-green tint. In the microscopic image, it sometimes forms a diablastic texture according to the (100) miller index. It is usually found near micas represented by muscovite, lepidolite, and, less often, biotite ( Figure 5). The schist is highly visible. Small admixtures of Fe-oxides can be seen along the schistosity of the rock. The straw color on the thin section has a clear, positive relief, with darkening extinction. Lepidolite forms large lamellar aggregates, usually colored pearly pink. Macroscopically, this mineral forms flakes reaching up to 1cm in size. It is usually quite visible in the rock due to its coloration and luster. In the microscopic image, it forms numerous adhesions of varying sizes. It is present with spodumene, near plagioclase and quartz. Between the mica flakes, rutile be observed. In the thin section, it is colorless, with a faint, negative relief. Under polarized light, it shows second-order interference colors, optically resembling biotite ( Figure 6). Our microscopic observations of lepidolite showed some deformation of its lamellae due to dynamic processes.  Fuchsite forms fine, scaly accumulations, the size of which reaches several millimeters. Macroscopically, it is colored green and has a pearly luster. It is highly visible against the background of biotite and feldspar in the investigated rocks. Fine zircon grains are visible in the background of the fuchsite aggregates ( Figure 7). In the microscopic image, they form polysynthetic adhesions with muscovite occurring between quartz and orthoclase. The sample shows pleochroism with a delicate greenish (β)-bluish (α) coloration. Under polarized light, it shows intense second-order interference colors, making it similar to muscovite.
Fuchsite forms fine, scaly accumulations, the size of which reaches several millimeters. Macroscopically, it is colored green and has a pearly luster. It is highly visible against the background of biotite and feldspar in the investigated rocks. Fine zircon grains are visible in the background of the fuchsite aggregates ( Figure 7). In the microscopic image, they form polysynthetic adhesions with muscovite occurring between quartz and orthoclase. The sample shows pleochroism with a delicate greenish (β)-bluish (α) coloration. Under polarized light, it shows intense second-order interference colors, making it similar to muscovite.

Spectroscopic Properties of the Minerals under Investigation
Infrared studies carried out for spodumene showed some small oscillations at a wavelength of 3612 cm −1 , which can be explained by the influence of water. Values in the vicinity of 1005 cm −1 may be related to stretching vibrations for silicon-oxygen tetrahedra [74]. Vibrations in the vicinity of 779 cm −1 can be correlated with Si-O stretching vibrations. Similarly, for lengths of 647 cm −1 to 448 cm −1 , non-bridging bending vibrations for O-Si-O can be found with the participation of aluminum, which can also substitute the spodumene structure in an octahedral position ( Figure 8). The latter oscillations are also affected by the position of lithium (448 cm −1 ), which, combined with oxygen, contributes to their modification. Through a comparison with the crystals of jadeite, it can be seen that substitution with Na cation with an ionic radius of 186 pm [75] in the M6 position shifts these vibrations to 455 cm −1 . In comparison, magnesium enstatite, in the M6 position, has 447 cm −1 vibrations (enstatite [76] and bronzite [77]). Lithium is a much lighter element than sodium, as its molar mass is 6.941 (for sodium it is 22.989 [51,78] close parenthesis g/mol) and its ionic radius is 152 pm. The full width at half maximum of the 455 cm −1 vibrations suggests that these vibrations are partly derived from the sodium at this position.

Spectroscopic Properties of the Minerals under Investigation
Infrared studies carried out for spodumene showed some small oscillations at a wavelength of 3612 cm −1 , which can be explained by the influence of water. Values in the vicinity of 1005 cm −1 may be related to stretching vibrations for silicon-oxygen tetrahedra [74]. Vibrations in the vicinity of 779 cm −1 can be correlated with Si-O stretching vibrations. Similarly, for lengths of 647 cm −1 to 448 cm −1 , non-bridging bending vibrations for O-Si-O can be found with the participation of aluminum, which can also substitute the spodumene structure in an octahedral position ( Figure 8). The latter oscillations are also affected by the position of lithium (448 cm −1 ), which, combined with oxygen, contributes to their modification. Through a comparison with the crystals of jadeite, it can be seen that substitution with Na cation with an ionic radius of 186 pm [75] in the M6 position shifts these vibrations to 455 cm −1 . In comparison, magnesium enstatite, in the M6 position, has 447 cm −1 vibrations (enstatite [76] and bronzite [77]). Lithium is a much lighter element than sodium, as its molar mass is 6.941 (for sodium it is 22.989 [51,78] close parenthesis g/mol) and its ionic radius is 152 pm. The full width at half maximum of the 455 cm −1 vibrations suggests that these vibrations are partly derived from the sodium at this position. In the case of the study micas (fuchsite and lepidolite, Figure 9), comparisons were made with muscovite [79]. In both cases, the absorbance characteristic of stretching vibrations of the OH groups in the vicinity of 3625 and 3608 cm −1 is visible (Figure 9). These are determined by vibrations between ions located in octahedral groups and their interaction with water [80,81]. These differences become apparent depending on the nature of the ions in the analyzed minerals (Li in lepidolite, Cr in fuchsite). There is also a slight increase In the case of the study micas (fuchsite and lepidolite, Figure 9), comparisons were made with muscovite [79]. In both cases, the absorbance characteristic of stretching vibrations of the OH groups in the vicinity of 3625 and 3608 cm −1 is visible (Figure 9). These are determined by vibrations between ions located in octahedral groups and their interaction with water [80,81]. These differences become apparent depending on the nature of the ions in the analyzed minerals (Li in lepidolite, Cr in fuchsite). There is also a slight increase in absorbance in the region of 1621 cm −1 , which is more pronounced for lepidolite. Another oscillation in the region of 970 cm −1 and 960 cm −1 is related to deformations produced through connection between aluminum and the OH group in these minerals [82].

Fuchsite
The studied fuchsite crystals, like all minerals in this group, contain chromium [82,83]. This is visible in the results of the diffraction measurements for the monocrystals and XPS. The X-ray data indicate that the studied fuchsite crystal contains 0.4 ions of this element per elemental cell of the crystal in the Cr-Al layer ( Figure. 7). It is worth noting the staggered position of both the Al 3+ and Cr 3+ ions at a distance of 0.12(1) Å (Figures 10  and 11). This spread is due to the difference in the ionic radii of these two elements. The diffraction data show that only one position in the lattice, where the Al 3+ ions are present, is occupied by additional Cr 3+ ions, while the other position is 100% occupied by Al 3+ ions ( Figure 10). In addition, the layer has a free space filled, in this case, with water or an OHgroup in the amount of 0.1 molecule/ion per elementary cell. In this case, the OHgroup can compensate for the positive charge of the cations. In the Si-K layer, no admixture of other ions is observed at the detection level of this technique. All cell parameters and com-

Fuchsite
The studied fuchsite crystals, like all minerals in this group, contain chromium [82,83]. This is visible in the results of the diffraction measurements for the monocrystals and XPS. The X-ray data indicate that the studied fuchsite crystal contains 0.4 ions of this element per elemental cell of the crystal in the Cr-Al layer (Figure 7). It is worth noting the staggered position of both the Al 3+ and Cr 3+ ions at a distance of 0.12(1) Å (Figures 10 and 11). This spread is due to the difference in the ionic radii of these two elements. The diffraction data show that only one position in the lattice, where the Al 3+ ions are present, is occupied by additional Cr 3+ ions, while the other position is 100% occupied by Al 3+ ions ( Figure 10). In addition, the layer has a free space filled, in this case, with water or an OHgroup in the amount of 0.1 molecule/ion per elementary cell. In this case, the OHgroup can compensate for the positive charge of the cations. In the Si-K layer, no admixture of other ions is observed at the detection level of this technique. All cell parameters and compositions are within the typical limits for this type of mineral. The thermal vibration ellipsoids observed in the experiment at 296 K had small thermal vibration amplitudes of U iso 0.02-0.03 ( Figure 11). This indicates strong interactions between ions in the lattice.

Lepidolite
Diffraction studies of the lepidolite yielded its structure [84][85][86][87]. They confirmed that it is a mineral from the silicate cluster, classified as lithium micas with an admixture of

Lepidolite
Diffraction studies of the lepidolite yielded its structure [84][85][86][87]. They confirmed that it is a mineral from the silicate cluster, classified as lithium micas with an admixture of  Figure 11. Crystal structure of the fuchsite from the analyzed rocks, as received by the authors (a, b, c-the main structural axes).

Lepidolite
Diffraction studies of the lepidolite yielded its structure [84][85][86][87]. They confirmed that it is a mineral from the silicate cluster, classified as lithium micas with an admixture of Fe 2+ or Mn 2+ in one position. However, unequivocally determining which ion is in this position is impossible with this technique. Positively charged Li-K ions reside in the space between the negatively charged aluminosilicate layers. In addition, OH − group or water molecules in the amount of 0.1 per elementary cell of the crystal can be found in this crystal net space ( Figure 12). In an elementary cell, there are three such layers in the direction of b. A richer atomic composition is provided by the data obtained through XPS measurements. This technique is more sensitive to heavier elements and allows for the unambiguous determination of their type. In contrast, lithium ions, which are difficult to determine via XPS, are visible in the monocrystalline structure. The ratio of K/Li ions is 2:1 in the structure. A close fit of the X-ray data with the model indicates that the lattice occupancy of Al 3+ ions is 90 ± 5%. This indicates that aluminum shares this position with lighter ions, e.g., Mg and Na. However, (Figure 10), in this case, it is necessary to properly balance the charges in the lattice. Also, the occupancy of the Li position is less than 100%, which, in this case, may indicate the partial substitution of this position with water molecules. The low values of the Q izo parameters (0.02-0.03) for atoms at 296 K indicate strong interactions between atoms ( Figure 13). of b. A richer atomic composition is provided by the data obtained through XPS measurements. This technique is more sensitive to heavier elements and allows for the unambiguous determination of their type. In contrast, lithium ions, which are difficult to determine via XPS, are visible in the monocrystalline structure. The ratio of K/Li ions is 2:1 in the structure. A close fit of the X-ray data with the model indicates that the lattice occupancy of Al 3+ ions is 90 ± 5%. This indicates that aluminum shares this position with lighter ions, e.g., Mg and Na. However, (Figure 10), in this case, it is necessary to properly balance the charges in the lattice. Also, the occupancy of the Li position is less than 100%, which, in this case, may indicate the partial substitution of this position with water molecules. The low values of the Qizo parameters (0.02-0.03) for atoms at 296 K indicate strong interactions between atoms ( Figure 13).

Spodumene
This is another studied mineral from the silicate cluster containing l In this case, the structural studies of the crystals indicated that the stoichio of Li and Al in the crystal lattice are within the error margin. Attempts to fit model with a free occupancy parameter for Li indicated that the modeled e at this site is slightly higher than 1, at 1.06 ( Figure 14). This may indicate of a heavier element at this site, e.g., sodium, as suggested by the XPS and ments. In the studied monocrystals, other ions were not visible in the crysta 12). In the spodumene, silicate ions connect adjacent layers, so there is no for additional ions between them, which explains the composition of th

Spodumene
This is another studied mineral from the silicate cluster containing lithium [88][89][90][91]. In this case, the structural studies of the crystals indicated that the stoichiometric contents of Li and Al in the crystal lattice are within the error margin. Attempts to fit a crystal lattice model with a free occupancy parameter for Li indicated that the modeled electron density at this site is slightly higher than 1, at 1.06 ( Figure 14). This may indicate a small content of a heavier element at this site, e.g., sodium, as suggested by the XPS and FTIR measurements. In the studied monocrystals, other ions were not visible in the crystal lattice ( Figure 12). In the spodumene, silicate ions connect adjacent layers, so there is not enough space for additional ions between them, which explains the composition of this mineral. The compact lattice structure also contributes to strong interactions between atoms, which, in turn, manifests itself in the lowest Q izo values of all the minerals presented (0.006-0.017) and its highest relative hardness (Figure 15).

Discussion
The minerals included in rocks found in northern Scandinavia (within Norway, Finland, and Russia) [92][93][94][95][96][97] were studied. These are exposed in many places in the area under discussion. Due to their mineralization, they may be significant in terms of raw material development, although the relatively small size of these pegmatite veins makes their profitability highly dependent on raw material prices. The mineralization of these pegmatites is the result of the crystallization of residual melts, which contain many incompatible

Discussion
The minerals included in rocks found in northern Scandinavia (within Norway, Finland, and Russia) [92][93][94][95][96][97] were studied. These are exposed in many places in the area under discussion. Due to their mineralization, they may be significant in terms of raw material development, although the relatively small size of these pegmatite veins makes their profitability highly dependent on raw material prices. The mineralization of these pegmatites is the result of the crystallization of residual melts, which contain many incompatible elements [55,98]. On the other hand, the presence of some elements is related to the chemistry of the host rocks. This is particularly evident in the case of fuchsite, in which the presence of chromium may be related to specific rock types. Such small occurrences of fuchsite have been found by the authors in vein rocks in the Monchepluton area (Russia). Lepidolite and spodumene, on the other hand, show small admixtures of sodium, manganese, and iron, which may also be related to the rocks near these pegmatites. This was confirmed by both micro-area studies and monocrystal and XPS analyses. The presence of water in the mica and even in the spodumene (found using FTIR) confirms the hydrothermal nature of the association between these minerals [99,100]. Their nature in the discussed rocks varies. Optical studies indicated that the spodumene in the analyzed pegmatites usually has hypidiomorphic crystals, which may indicate crystallization as an early silicate phase. The presence of small admixtures of sodium may indicate that the mineral originally formed at a great depth, where higher pressures prevail, and then tectonically dislocated with solutions to its present site of occurrence, where it was hydrothermally altered [53,54,57]. On the other hand, aggregates of fuchsite and lepidolite tend to be secondary, co-occurring with other micas and occupying a position in the interstices of existing minerals; moreover, lepidolite can probably be a secondary mineral, formed at the expense of spodumene, as evidenced by our observations of this mineral in pegmatites. It is noteworthy that in addition to these minerals, there are many accessory phases, such as apatite and zircon. Alongside these, opaque minerals are present in large numbers. The presence of tin minerals points to the granitoid association as the source material for the origin of the schists [101,102]. In the case of the LCT pegmatites found in the Kaustinen area, these include, in addition to the aforementioned cassiterite and barite, magnetite, ilmenite, and titanite, as well as galena, sphalerite, and chalcopyrite. The presence of these minerals may also be related to the granitoid products and the action of hydrothermal products. The mineralization of Kolmozero pegmatites is also associated with the action of hydrothermal formations. This is evidenced by the mutual relations of rock-forming minerals with the observed bixbite, clarkeite, and sillenite, which are also accompanied by magnetite. Columbite and tantalite were also found in the LCT pegmatites.

Conclusions
The studied minerals are from selected rocks that are exposed in northern Scandinavia. The studied mineralization indicates the hydrothermal nature of these components. The studied minerals, including spodumene, lepidolite, and fuchsite, were formed after residual crystallization. The small admixtures of sodium present in the spodumene may indicate that it was formed under high pressures and, together with the melt, reached its present location, where it was altered due to pressure from hydrothermal fluids. The occurring lepidolite crystallized at a later stage, at the expense of spodumene, as evidenced by the structure of this mineral in the rock and by association (the occurrence of relics of spodumene in the vicinity of lepidolite). Fuchsite, like lepidolite, crystallized in the final stage, co-occurring with muscovite and biotite. The presence of chromium ions in this fuchsite is probably due to the occurrence of chromium-containing rocks in the vicinity of the formation of intrusions from the residual melts in which the studied rocks crystallized. The presence of accessory and opaque minerals also attests to the granitoid association of the original solutions. The minerals present may be of economic importance. Thorough research may contribute to the discovery of new locations of this type of pegmatite in the discussed area. Funding: We would like to thank EcoTech Complex in Lublin for providing the equipment for the X-ray diffraction measurements.