Cause Of Color Research Articles

Atomic resolution transmission electron microscopy visualisation of channel occupancy in beryl in different crystallographic directions

The causes of colour in beryl have been a research topic for decades. For some varieties, such as emerald (green, coloured by Cr3+ and/or V3+), the main cause of colour is substitutions by metal atoms within the framework. However, the causes for the yellow and blue colours in heliodor, golden beryl and aquamarine are still debated. It is generally agreed that Fe ions are responsible for the colour, but there are differing conclusions about the valence states of these ions, the occupied positions and the colour-inducing processes involved. The colour of aquamarine is commonly attributed to intervalence charge transfer (IVCT) between Fe3+ and Fe2+. Various combinations of sites have been proposed to host the Fe ions engaging in this IVCT. Here we present a new approach to address the topic of colour generation: atomic resolution scanning transmission electron microscopy (STEM). For the first time, atomic resolution images of a beryl (natural aquamarine) are presented in the three crystallographic directions [0001], [1-210] and [1-100]. Ions are clearly resolved in the channels. From the ratio of channel occupation and the correlation of the atoms per formula unit (apfu) calculations we conclude that Fe resides in the framework, not in the channels. The projections in the [1-210] direction directly show that the cavity channel site 2a is occupied, most likely by Cs, in agreement with recent results in the literature.

New Insights for Gem-Quality Mn-Bearing Diopside-Omphacite, Violane Variety, from Saint Marcel (Val D’Aosta, Italy): Its Trace Elements and Spectroscopic Characterization

This study proposes new data on the rare pyroxene, variety violane, sampled from its type locality, Praborna manganese deposit, near Saint Marcel (Val d’Aosta, Italy). Violane is very appreciated as a gemstone for its different hues of violet-blue color and is characterized by its diopsidic or omphacitic composition. To assess the possible causes of color, electron-probe microanalysis (EMPA) and laser-ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) were used to establish the chemical composition. Raman and Fourier transform infrared (FTIR) spectroscopy, ideal for the non-destructive analysis, identified the different present phases directly on gemstone. Raman and FTIR spectra highlighted the presence, in the same sample, of diopside and omphacite showing almost inappreciable violet hue difference. The two minerals were easily differentiated by microprobe analyses and showed a compositional heterogeneity not linked to the different colors. The best way to detect the color-causing elements in microcrystalline violanes resulted in the analysis of trace elements and their quantification. An enrichment of Ti and Li characterizes darker violet omphacite and that of V and rare-earth elements (REE) the lilac-lavender or light violet-blue diopside. In general, our results led us to say that the color changes, previously proposed as due to Mn both in divalent and trivalent oxidation state, may be controlled by trace elements or by concentration of minor elements, such as Fe, and their oxidation state. REE patterns showed a negative anomaly of Ce that could be ascribed to the variation of the oxygen chemical potential occurring in the ore. The new data, combined with previous results, may provide new constrains on the processes that generated the Mn-rich deposit of Praborna.

Timing of formation and cause of coloration of brown nephrite from the Tiantai Deposit, South Altyn Tagh, northwestern China

The world’s largest and economically valuable nephrite deposits are distributed along the Western Kunlun Orogen in northwestern China. During the past 20 years, extensive white and brown nephrite deposits have been discovered in both China and Russia, and several of these deposits have been found in South Altyn Tagh in the eastern part of the Western Kunlun Orogen. However, the timing of formation, genesis, petrographic characteristics, mineralogical composition, and reasons for the white–brown color of the nephrite remain unclear. We analyzed 50 samples of white, brown, and white–brown nephrite from the Tiantai nephrite deposit in Qiemo County with the aim of understanding the processes of formation, age, and diversity of these nephrites. Three main types of nephrite can be distinguished: white, brown, and dark brown. X-ray diffraction and petrographic studies indicate that the brown and dark-brown nephrite samples have fewer mineral inclusions compared with the white nephrites. The nephrite formed during early retrogression through the sequence of diopside skarn → coarse-grained tremolite skarn and coarse-grained tremolite → fine-grained tremolite. The higher bulk Fe content of the white nephrite (0.76 wt% FeO) relative to the brown nephrite (0.39 wt%), and the uniform, very low Fe2O3 contents of both of these color varieties (<0.15 wt%), suggest that the brown coloration is unrelated to Fe content and oxidation state. The white nephrite is characterized by a wide range of SiO2 contents (49.6–56.7 wt%), in contrast to the brown nephrites, which are characterized by nearly constant SiO2 contents (~58 wt%), close to the ideal content for tremolite. On average, the white nephrite is enriched in Al2O3 (3.22 wt%) and water (3.96 wt% loss on ignition) and depleted in CaO (12.35 wt%) relative to the brown nephrite (0.80 wt% Al2O3, 2.23 wt% loss on ignition, 12.95 wt% CaO). These characteristics, combined with greater transparency and higher Al and water contents in the chlorite formula relative to that of tremolite, as well as a near-absence of Ca in the chlorite formula, can explain the lower transparency and associated more intense coloration (i.e., yellow to brown) of the brown nephrite in terms of the lower modal abundance of chlorite. The spatial distribution of selected elements agrees with this hypothesis, whereby the brown-colored zones are dominated by Ca- and Sr-rich (substituting Ca) domains reflecting the highest modal volume of the tremolite. In contrast, the white zones are characterized by a substantially higher volumetric ratio of Al-rich domains, reflecting the higher chlorite content. Thus, the different coloration is not caused by specific elements, but by modal proportions of tremolite and chlorite. The slightly higher average Cr (10.1 ppm) and Ni (6.4 ppm) contents of brown nephrite, relative to white nephrite (8.7 ppm Cr and 5.5 ppm Ni), might also contribute to the color intensity and brown coloration. Ore-forming fluids involved in the formation of the studied nephrite have isotopic compositions of δ18O = 1.5‰ to 9.4‰ (330–430 °C) and δD = −87‰ to −50‰ (330–450 °C), suggesting that the formation of the Mg-skarn deposit was related to metasomatism of dolomite by fluids derived from local granite/granodiorite intrusions. Zircons from three brown–white samples yield concordant SHRIMP ages of 438 ± 14 Ma (2σ, MSWD=10.4), 916 ± 10 (2σ, MSWD = 1.5), 438 ± 9 Ma (2σ, MSWD = 5.3), and 431.1 ± 2.5 Ma (2σ, MSWD = 2.4). The younger ages (ca. 430 Ma) are close to those for placer nephrite from the Yurungkash and Karakash rivers, as well as those for Yecheng, Alamas, and Buya granodiorites, and probably represent the primary formation ages of nephrite within the Hetian Nephrite Belt. Overall, these ages indicate that the primary deposits formed during pre- or post-orogenic stages in the Western Kunlun Orogen. 40Ar/39Ar dating of hydrothermal muscovite and phlogopite intergrown with tremolite in the nephrite yielded ages of 418.8 ± 3.4 Ma (2σ, MSWD = 0.65), 379.5 ± 3.0 Ma (2σ, MSWD = 0.81), and 354.5 ± 3.6 Ma (2σ, MSWD = 0.71), which suggest multiple metasomatic activity. The similar formation ages of nephrites from Altyn Tagh (433 Ma) and from the previously studied areas of West Kunlun (441–378 Ma) and East Kunlun (416 Ma) indicate that these nephrites formed during the closure of the Proto-Tethys and in the accompanying post-collisional extensional environment.

Characteristic of Fe in tektite observed from XANES and UV-Vis spectroscopy

Tektite is a geological sample formed as a result of a collision of the meteorite on the surface. An energy from the collision results in an excavation of the melted material into the Earth’s atmosphere and landed back on the surface further away from the impact site having glassy or crystalline textures. Tektite was deposited in Thailand and was identified as part of the Australasian strewn field. Chemical compositions of tektites have previously been studied. However, there is no study has established a relationship between composition and color of tektites. Thus, this study aims to relate the characteristic of color-center element, Fe, to the color of tektites using X-ray Absorption Near Edge Structure (XANES) and UV-Vis spectroscopy. Nine tektite samples were collected from Korat plateau and purchased from Thailand and Vietnam gem markets. XANES spectra of all (nine) samples show similar Fe K-edge pattern with pre-edge and E0 at 7080-7089 and 7118 eV, respectively. The spectrum is 100 percent matched with XANES structure of FeO standard suggesting Fe component of Fe2+ oxidation state in the sample. Seven, out of nine, samples establish similar UV-Vis broad absorption peak at 492-539 nm, which corresponds to absorption peak of Fe2+. The UV-Vis absorption spectrum cannot be obtained from two samples possibly due to high Fe-content in the samples. The calculated energy band gaps (E g ) of the samples are in between 1.35 eV to 1.76 eV with maximum absorption in between 1.88 eV to 1.95 eV. The result is in consistent with a black color of the tektite. It indicates that cause of color in tektites is related to Fe-content and can be explained by the energy band. This study can be furthered compare with moldavite (green variety of tektite) in order to identify cause of color in impact-related materials like tektites, as well as to provide information for identification of synthetic and genuine moldavites and also for characterization of tektites sources using the component of various Fe oxidation states.

Study on the effect of heat treatment on amethyst color and the cause of coloration

The effect of heat treatment on amethyst color was studied from a new perspective of chromaticity of gemstones and the cause of amethyst coloration was discussed based on the results of X-ray diffraction, ultraviolet–visible spectroscopy. The results show that the amethyst color has no significant relationship with cell parameters but the crystallinity index decreases as temperature rises. The absorption band at 545 nm in the UV–visible spectrum can be related to a charge-transfer transition of Fe3+ and O2−, which has a significant relationship with amethyst lightness and chroma. The color at different temperatures can be divided into three stages: The amethyst stage with temperature below 420 °C, the prasiolite stage with temperature between 420 and 440 °C where the color center is the most unstable, the citrine stage with temperature above 440 °C. The color change degree of heated amethyst is related to its initial color. When the initial color is darker, the color difference of heated amethyst is larger, and the easier it is to change the color after heat treatment. A more appropriate heating temperature to obtain citrine by heating amethyst is about 560 °C.

Trace elements content and cause of color in ancient treated carnelian and its natural counterpart from SE Asia

Iron Age treated carnelian beads and their natural counterparts from SE Asia have been discussed in terms of attribution of transition and lighter elements in their matrix. They were investigated by using synchrotron techniques (XRF: X-ray fluorescence, XANES: X-ray absorption near edge structure, and XPS: X-ray photoelectron spectroscopy) and SEM-EDS: scanning electron microscope-energy dispersive spectroscopy. Ferrihydrite or ferrihydrite + goethite have been found as the causes of color. The treated stones were subjected to the sugar + sulfuric acid treatment of about 1800-year BP. This work has fulfilled information about the treatment in the ancient chalcedony to the archeomineralogy archive.

Is it possible to see darkness? Goethe and Aristotle on the role of light and darkness in vision

J.W. Goethe in his Farbenlehre deduced all physical colors from a simple primordial phenomenon that takes place every time light and darkness act through a semi-transparent colorless medium either on our eyes or on the opposite surfaces. This basic rule of Goethe’s color theory was criticized by his contemporary physicists, who argued that darkness could not play an active role in the origin of colors because of being a mere absence of light. The paper demonstrates that this criticism became possible only if one shares the Newtonian view on the nature of light and darkness. Goethe however held a more traditional point of view, which he traced back to Antiquity and Aristotle. In contrast to Newton and his followers, previous scientists considered light not as an immediate cause of colors but as an actually transparent medium that conveyed colors from the visible objects to the organ of sight. For vision to take place, the color must first affect the light, which in its turn, must affect the faculty of vision. Though it is difficult to say what kind of change the light undergoes when some colored object is seen through it, most Aristotle commentators agree that this change must be real and not mere relational. In Aristotle’s physics, however, things that are capable of acting on and being affected by one another are either contraries or consist of contraries. Therefore, to be visible the color must be either dark or to contain darkness. Thus, assuming that Goethe shared the Aristotelian concept of light, we have to conclude that he was not mistaken saying that darkness "acts” upon our eyes or “is seen through” the illuminated semi-transparent medium.

Impurity and radiation defects in LiB3O5 crystals. The nature of centers in LiB3O5 crystals, which are responsible for coloration during the long-term operation of optical elements

An attempt is made to explain the causes of coloration of LiB3O5 crystals after their long-term operation as laser elements. By EPR and optical spectroscopy the impurity and radiation centers are studied in as-grown LiB3O5 crystals and in the crystals whose color appeared after the long-term operation as laser elements. In a number of as-grown crystals a copper impurity is detected. EPR spectral parameters and the structural positions of Cu2+ ions are found. Defect formation features in electron irradiated as-grown LiB3O5 crystals and in the most colored regions of crystals of spent laser elements are analyzed. It is shown that in both growth crystals and crystals after long-term operation as laser elements the same set of radiation defects is observed: oxygen O– in the interstitial position, an O– hole center in the crystal structure, and the B2+ electron center due to the removal of an oxygen atom near the lithium vacancy. The only distinction is that the concentration of these radiation defects in crystals long used as laser elements is higher than that in growth ones by an order of magnitude. The results obtained enable the conclusion that the cause of coloration of LiB3O5 crystals is photo-induced diffusion of lithium atoms and their capture by cation vacancies in the dark part of the crystal, which provides the formation and accumulation of lithium vacancies in the region where the laser beam passes.

Spectroscopic properties for identifying sapphire samples from Ban Bo Kaew, Phrae Province, Thailand

Gemstone commercial is a high revenue for Thailand especially ruby and sapphire. Moreover, Phrae is a potential gem field located in the northern part of Thailand. The studies of spectroscopic properties are mainly to identify gemstone using advanced techniques (e.g. UV-Vis-NIR spectrophotometry, FTIR spectrometry and Raman spectroscopy). Typically, UV-Vis-NIR spectrophotometry is a technique to study the cause of color in gemstones. FTIR spectrometry is a technique to study the functional groups in gem-materials. Raman pattern can be applied to identify the mineral inclusions in gemstones. In this study, the natural sapphires from Ban Bo Kaew were divided into two groups based on colors including blue and green. The samples were analyzed by UV-Vis-NIR spectrophotometer, FTIR spectrometer and Raman spectroscope for studying spectroscopic properties. According to UV-Vis-NIR spectra, the blue sapphires show higher Fe3+/Ti4+ and Fe2+/Fe3+ absorption peaks than those of green sapphires. Otherwise, green sapphires display higher Fe3+/Fe3+ absorption peaks than blue sapphires. The FTIR spectra of both blue and green sapphire samples show the absorption peaks of –OH,-CH and CO2. The mineral inclusions such as ferrocolumbite and rutile in sapphires from this area were observed by Raman spectroscope. The spectroscopic properties of sapphire samples from Ban Bo Kaew, Phrae Province, Thailand are applied to be the specific evidence for gemstone identification.

Human Colors-The Rainbow Garden of Pathology: What Gives Normal and Pathologic Tissues Their Color?

- Colors are important to all living organisms because they are crucial for camouflage and protection, metabolism, sexual behavior, and communication. Human organs obviously have color, but the underlying biologic processes that dictate the specific colors of organs and tissues are not completely understood. A literature search on the determinants of color in human organs yielded scant information. - To address 2 specific questions: (1) why do human organs have color, and (2) what gives normal and pathologic tissues their distinctive colors? - Endogenous colors are the result of complex biochemical reactions that produce biologic pigments: red-brown cytochromes and porphyrins (blood, liver, spleen, kidneys, striated muscle), brown-black melanins (skin, appendages, brain nuclei), dark-brown lipochromes (aging organs), and colors that result from tissue structure (tendons, aponeurosis, muscles). Yellow-orange carotenes that deposit in lipid-rich tissues are only produced by plants and are acquired from the diet. However, there is lack of information about the cause of color in other organs, such as the gray and white matter, neuroendocrine organs, and white tissues (epithelia, soft tissues). Neoplastic tissues usually retain the color of their nonneoplastic counterpart. - Most available information on the function of pigments comes from studies in plants, microorganisms, cephalopods, and vertebrates, not humans. Biologic pigments have antioxidant and cytoprotective properties and should be considered as potential future therapies for disease and cancer. We discuss the bioproducts that may be responsible for organ coloration and invite pathologists and pathology residents to look at a "routine grossing day" with a different perspective.

Spectroscopy of red dravite from northern Tanzania

Low-Fe dravite with a formula of Na0.66Ca0.16Mg2.62Fe0.33Mn0.02Ti0.02Al5.95B3Si6.04O27(OH)4 is described from Engusero Sambu, northern Tanzania (On maps, Engusero Sambu may be found to be marked as belonging to Kenya, but in reality, it is located near the border in northern Tanzania). The sample has an unusual red color that is distinctly different from the red dravite from the Osarara, Narok district, in Kenya that was formerly studied by Mattson and Rossman (Phys Chem Miner 14:225–234, 1984) and Taran and Rossman (Am Mineral 87:1148–1153, 2002). This unique sample has been characterized by optical and Mossbauer spectral measurements to investigate underlying cause of the intense bands in absorption spectra that give rise to the red color. These features are shown to be caused by exchange-coupled Fe3+–Fe3+ interactions. Thermal annealing of the samples causes an increase in Fe3+ contents due to oxidation of [Y]Fe2+. However, heat treatment does not change the high-energy absorption edge, which is probably caused by intense ligand-to-Fe3+ charge-transfer UV bands. In fact, Mossbauer results show that high-temperature annealing initiates breakdown of the tourmaline into an Fe oxide and causes accompanying redistribution of Fe3+ within the structure. Because of the popularity of tourmaline as a gemstone, this work has implications for understanding the causes of color in tourmaline, facilitating recognition of the distinctions between naturally occurring and treated tourmalines in the gem industry and enabling heat treatments for color enhancement.

개념수채화를 반영한 스티븐 홀 작품의 공간색채 연구

Contemporary architecture is philosophy and art, and science are different that holds the architecture of human thought and behavior based on a variety of physical space. In addition, the technology is used by the new media graphics, lasers, LED, which were possible only in imagination, using tools such as the time-space of the potential for explosion. In particular, it was found in the spacial color of atypical using the nature of light. Such these architecture is space people actively experiencing a sense towards the expansion of its place. Therefore, the study purpose is to explore the Steven Holl's spacial colors to utilize the space is important to the possibility of light. He prefers the connection to the invisible world is inferred from the visible world and other space. He thoughts an idea linked to the concept watercolors which is a tool that holds to the notion of the flexibility of light and shadow. Concept watercolor is the idea space, establish space, recombinant space, and the growthy space. These have shown the no fixed spacial color cause of the combination of the different tones according to the characteristics of the mixed-color development of a concept watercolors demonstrated the spacial color of the replacement. That is to establish a parody of the works light blending spacial color.

Measurements and modelling of the influence of dentine colour and enamel on tooth colour

ObjectivesWe provide a quantitative predictive model for the extent to which coloured dentine, visible through the enamel, contributes to tooth colour. Our model uses (L*,a*,b*) measurements rather than spectral measurements. MethodsWe have used a model system, composed of a slice of bovine enamel placed on top of coloured paper. We have measured the colour of the enamel–paper combination, as an analogue for a tooth, and have related this to the colour of the paper, as an analogue for dentine. By changing the paper colour, we have been able to explore how the colour of dentine determines tooth colour, according to our model system. We have also compared hydrated and desiccated samples. ResultsIn qualitative terms, superimposing the enamel on top of the paper increases the “lightness” for all colours tested except white while simultaneously reducing the chromaticity, a measure of the extent to which the colour differs from grey. Desiccated enamel is much more effective at increasing the lightness and reducing the chromaticity than hydrated enamel. Quantitatively, our measurements are reproduced by the mathematical model we have developed to within 2% in “lightness” and about 8% in chromaticity. ConclusionsWe are able to predict the colour of an analogue for a tooth, composed of bovine enamel and coloured paper, from the colour of an analogue for the dentine, the coloured paper alone, with good accuracy. This understanding provides insights into the role of dentine colour in determining tooth colour. Clinical SignificanceOur work helps quantify the importance of dentine colour, compared to other, extrinsic causes of colour, such as staining, in determining the visible colour of teeth. Our predicted colours represent a baseline to which extrinsic sources will add.

Mechanisms of Color Production in a Highly Variable Shield-Back Stinkbug, Tectocoris diopthalmus (Heteroptera: Scutelleridae), and Why It Matters

Theory suggests that aposematism, specifically the learned avoidance of unprofitable prey via memorable color patterns, should result in selection for pattern uniformity. However, many examples to the contrary are seen in nature. Conversely, honest sexual signals are likely to exhibit greater variation because they reflect underlying variation in mate quality. Here we aim to characterize and quantify the mechanistic causes of color in Tectocoris diopthalmus to shed light on the costs of color production, and thus the potential information content of its color signals. We use Tectocoris diopthalmus because it is a weakly-defended stinkbug, and presents elements that have classically been studied in the context of aposematism (red coloring), and sexual selection (sexual dichromatism and iridescent coloring). Pigment analysis reveals that variation in orange coloration is due to the amount of erythropterin pigment, stored in intracellular granules. This pigment is common in Heteroptera, and as an endogenously produced excretory byproduct is unlikely to reflect mate quality or variation in unprofitability of the bug. Electron microscopy reveals the iridescent patches are caused by an epicuticular multilayer reflector, and the hue and patch size are directly related to the layer widths and extent of coverage of this layering. Furthermore, we identified melanin as an essential component of the multilayer reflector system; therefore, the quality of the iridescent patches may be affected by aspects of rearing environment and immunocompetence. We posit that T. diopthalmus has co-opted the melanic patches of a ‘typical’ red and black aposematic signal, transforming it into a complex and variable iridescent signal that may enhance its capacity to display individual quality.

9,10-アントラキノンを溶解したポリ乳酸のフォトクロミズムの検討

The color change from pale yellow to vermilion due to the UV-irradiation and the reverse color change due to the heating at about the glass transition temperature (Tg) were investigated for the poly(lactic acid) (PLA) mixed with 9,10-anthraquinone (AQ) by electronic absorption and IR analysis. The absorption of the broad band around 485 nm assigned to the electron donor acceptor (EDA) between AQ and anthrahydroquinone (AQH2) was increased by UV-irradiation and was decreased by the heating at about the glass transition temperature. The color change and reversion was possible by repeating the UV irradiation and the heating operations. A decrease of AQ and a formation of AQH2 by the UV irradiation and a increase of AQ and a small decrease of AQH2 by the heating were observed from the IR measurements. The formation of the AQ-AQH2EDA complex which hydrogen bonded with PLA was a cause of coloration and the dissociation of EDA was a cause of fading. At the same time, some of AQH2 was oxidized to AQ.

Color Vision: Appearance Is a Many-Layered Thing

The color of a surface changes when it is surrounded by other colors. A new illusion shows these changes are much stronger when seen through other colors as transparency, suggesting the brain parses the causes of color into separate layers.

Characterization of pink diamonds of different origin: Natural (Argyle, non-Argyle), irradiated and annealed, treated with multi-process, coated and synthetic

One of the commercial challenges today in the gem industry is to quickly identify the origin of color in pink diamonds — natural, treated and synthetic by use of standard and advanced gemological instruments. An analytical technique that is used by many gem labs involves UV fluorescence. The principle factors in the technique are the excitation wavelengths and the emission spectra. No systematic study of fluorescence of pink natural diamonds, pink treated and pink synthetic diamonds has been undertaken. This study is mainly focused on using fluorescence techniques to characterize pink diamonds and to compile a reference library of emission spectra. Longwave (LW) and shortwave (SW) fluorescence of 365, 254 and 220 nm illumination were used in a custom built microscope with a fluorescence camera to record images and a spectrometer to record spectral data with which to establish a correlation with the cause of color. Other advanced instruments (CL imaging, UV–VIS–NIR, FTIR, PL spectroscopy and electrical conductance) were used to establish additional criteria for distinguishing natural, treated and synthetic pink diamonds and to find a correlation with the “EGL USA CIS (Cross-reference Identification System) fluorescence method”.

Solar parameters of induced WO 3-coated glass

WO 3 films were prepared by sol–gel deposition process on Corning 2947, microscope slide substrates. The effects of irradiation on the solar parameters of WO 3 films were investigated between ∼1 and 21 kGy absorbed dose by Co-60 radioisotope. Three characteristic optical density bands explained the causes of color due to the absorption of sunlight at induced color centers of the transition elements such as W, Fe and Zr after the gamma irradiation. These bands lead to variations on the solar control in terms of shading coefficient. The absorbed dose plays a key role in the improvement of the shading coefficient dramatically, hence the solar parameters changed considerably depending on the induced color centers of the transition elements and the variations of the grains and the void sizes of the film. The results of the solar parameters of irradiated WO 3 films were compared with the unirradiated WO 3 films and uncoated corning in the solar range.

Luminescent, optical and color properties of natural rose quartz

Rose quartz is an interesting mineral with numerous impurities that have been studied by scanning electron microscopy (SEM), X-ray fluorescence (XRF), X-ray diffraction (XRD), cathodoluminescence (CL), ion beam luminescence (IBL), radioluminescence (RL), thermoluminescence (TL) and optical absorption (OA). After HF etching, rose quartz from Oliva de Plasencia (Caceres, Spain) shows under SEM the presence of other silicate phases such as dumortierite [ Al 6.5 - 7 ( BO 3 ) ( SiO 4 ) 3 ( O , OH ) 3 ] . The OA spectrum of rose quartz suggests that these inclusions are the cause of coloration of rose quartz. The luminescence (CL, IBL, RL, TL) spectra behavior, at both room temperature and lower, confirms that the ∼ 340 nm emission could be associated with Si–O strain structures, including non-bridging oxygen or silicon vacancy–hole centers; the observed ∼ 400 nm emission could be associated with recombination of a hole trapped adjacent to a substitutional, charge-compensated aluminum alkali ion center; the ∼ 500 nm emission could be associated with substitutional Al 3 + and the ∼ 700 nm peak could be associated with Fe 3 + point defects in Si 4 + sites. These results suggest that, while defect properties of rose quartz are not greatly dissimilar to those of purer forms of quartz and silica, further research seems necessary to determine criteria for the evolution of the newly-formed self-organized microstructures in the rose quartz lattice under irradiation.

Testing the relation between UV–vis color and TiO 2 content of the lunar maria

Reflectance spectroscopy is important for placing lunar samples into a regional and global geologic context. To this end, the ultraviolet–visible (UV–vis) color ratio, used to estimate the TiO 2 composition of mature mare basalts, has been one of the most widely used spectral parameters in lunar exploration. We examine the correlation between UV–vis color and TiO 2 content using a combination of Clementine, Lunar Prospector, and sample data to document the extent to which color is dependent upon TiO 2. Examination of the remotely sensed data reveals that the correlation between UV–vis ratio and TiO 2 composition is best represented by a sigmoidal trend rather than the canonical linear or curvilinear correlation. With this information, we are then able to evaluate between two models that propose different explanations for the relationship between UV–vis color and TiO 2. The first model attributes the correlation between TiO 2 and UV–vis color to spectrally neutral opaques (i.e., ilmenite), while the other emphasizes the effect of Fe–Ti charge-transfer in lunar glasses and dual scattering mechanisms between high- and low-Ti basalts. We do not find evidence in the spectral data to support the occurrence of Fe–Ti charge-transfer in lunar glass as the principal cause for color in high-Ti basalts. The data also do not substantiate the existence of different scattering mechanisms (e.g., volume v. surface scattering) between high- and low-TiO 2 basalts. Instead, our analyses substantiate that the spectral effects of ilmenite exhibit a major influence over the UV–vis ratio. By including sample data we find that in addition to ilemenite/TiO 2 content, factors such as FeO content, ilmenite grain size, modal abundance of plagioclase, and the olivine-to-pyroxene ratio in a mare soils can influence the UV–vis continuum. These findings point to promising avenues of research that future UV–vis spectral techniques can exploit in order to yield more accurate TiO 2 estimates and potentially additional petrologic information.