Pressed Powder Pellets Research Articles

Simultaneous Bulk‐Rock Elemental and Boron Isotope Ratio Measurement Using LA‐ICP‐MS on Silicate Micro‐Particulate Pellets

We have established a method for the simultaneous measurement of element abundances and boron isotopic compositions of bulk‐rock silicate samples by laser ablation coupled to two different ICP‐MS instruments. Fifteen silicate reference materials were prepared as micro‐particulate pressed powder pellets (MP) for analysis. Approximately 1/5th of the ablated material was transported to a single‐collector ICP‐MS for elemental measurement, while 4/5ths were sent to a multi‐collector ICP‐MS for boron isotope ratio measurement. Compositions of different milling materials (agate, zirconium oxide, tungsten carbide, sintered corundum and silicon nitride) were measured for the evaluation of potential contamination during sample preparation. Determined element mass fractions are in agreement with literature values within ±20%. For boron isotope ratios, the matrix‐dependent background elevation across the m/z from 9.9 to 11, and the effect of ablation mass was quantified. Measured δ11B values of most reference materials are consistent with literature values within ±1‰. The intermediate measurement precision is ±0.3‰ for JB‐2 with 30 μg g−1 B and ±0.4‰ for JA‐2 with 21 μg g−1 B. A publically available, web‐based streamlit app was developed for data processing (https://zenodo.org/doi/10.5281/zenodo.11150471). This paves the way for combined, accurate and precise elemental and boron isotope ratio measurements of geological materials.

The historical Corrente gold deposit, Minas Gerais, Brazil: Geological characteristics and a reconnaissance study of nugget effect

Corrente is a historical underground working in Minas Gerais, Brazil, mined for gold in the nineteenth century, for which little geological information is available. Retrieval of unpublished exploration reports from the 1980s has enabled the recognition of a 7-km-long linear cluster of historical underground and open-cast workings, here referred to as the Cata Branca–Corrente goldfield. Gold production ceased at Cata Branca, the most economically relevant deposit of the goldfield, in 1844. Both Corrente and Cata Branca are auriferous quartz-lode deposits. Geological characteristics of the Corrente deposit are presented, as well as reconnaissance whole-rock analyses for Au using a variety of analytical methods, including conventional fire assay, atomic absorption spectrometry, instrumental neutron activation analysis and laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) on pressed-powder pellets (PPPs). Corrente is characterised as a gold-only deposit. The Corrente auriferous quartz lode, hosted in the Archaean greenstone belt sequence of the Rio das Velhas Supergroup, is extensively oxidised and has conspicuous wall-rock alteration to fine-grained muscovite. The resulting sericite phyllite shows overprint by low-temperature kaolinitisation, likely the product of wall-rock hydration mediated by acidic water derived from sulfide oxidation at depth, below the modern weathering zone. The Corrente gold deposit has a high nugget effect. Time-resolved results of LA–ICP–MS on PPPs indicate the presence of particulate gold even in barren kaolinitised wall-rock phyllite.

Major element analysis of geological samples with wavelength Dispersive X-ray Fluorescence (WDXRF) spectrometry using glass disks and pressed powder pellets

Major element analysis of geological samples with wavelength Dispersive X-ray Fluorescence (WDXRF) spectrometry using glass disks and pressed powder pellets

Evaluation of Refractory Metal Concentrations in Nano-Particulate Pressed-Powder Pellets Using LA-ICP-MS

Whole-rock geochemical analysis is a standard method to measure the chemical composition of ores. Analysis of refractory ore metals such as Ta and W typically requires fused bead and acid digestion followed by inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled mass spectrometry (ICP-MS). Since these techniques are time-consuming and expensive, there is a demand for methods that can quantitatively measure low elemental concentration of refractory ore metals using a less expensive and simple approach. This paper evaluates preparation and analytical procedures developed to obtain whole-rock element concentrations of ore samples and mineral concentrates. It shows that the production of nano-particulate pressed-powder pellets followed by LA-ICP-MS analysis of W and Ta ores can be used to determine, within the error margin, the concentrations of the refractory metals W, Ta, Nb, and Sn compared to a reference values obtained by solution analysis. The results have implications for developing a commercially viable method for analysis of refractory elements to benefit mineral processing given the simplicity and resource-efficiency of the combined pressed pellet production and laser ablation analytical methodology.

Machine learning and transfer learning for correction of the chemical and physical matrix effects in the determination of alkali and alkaline earth metals with LIBS in rocks

Alkali and alkaline earth metals incorporated in rocks can indicate past water activities. Their precise determination with laser-induced breakdown spectroscopy (LIBS) is required for geological investigations on Earth as well as on Mars. In previous studies, laboratory standard samples in the form of pressed powder pellets were used to train univariate or multivariate regression models. Although various chemical compositions of the used samples cover the chemical and mineralogical diversities of the rocks encountered in field measurements, the difference in physical forms between the laboratory standards and the real samples analyzed in situ leads to the physical matrix, which dramatically reduces the prediction performance of the models for real samples. The present work performs a systematic study of the influences of the chemical and physical matrix effects, and develops multivariate regression models based on machine learning and transfer learning to effectively correct these effects. The experiment involved a set of 27 fully characterized natural rocks. A part of each rock was prepared in a pressed powder pellet, while another part was left in its raw state. LIBS spectra recorded from pellets were first used to train multivariate regression models based on a machine learning approach combining feature selection and back-propagation neural network (BPNN). The trained models were tested respectively by independent pellets and raw rocks with and without counterpart pellets in the training sample set. An effective correction of the chemical matrix effect was observed for the models when tested with pellets. While the tests with raw rocks revealed the influence of the physical matrix effect on the prediction performance of the models. Transfer learning was then introduced by including a part of the raw rocks in the training sample set, leading to a significant improvement of the prediction performances for raw rocks, with root mean square errors of prediction (RMSEPs) of 1.6, 18, 101, and 162 wt. ppm respectively for Li, Rb, Sr, and Ba.

A Revision of the Sb-Te Binary Phase Diagram and Crystal Structure of the Modulated γ-Phase Field

A new experimental study of Sb-Te, based on long term annealed samples homogenized by intermediate powdering and re-annealing of the pressed powder pellets was performed. More than 25 samples were prepared, covering the entire composition range between 0 and 60 at.% Te. This part of the phase diagram was disputed for many years, as the number of phases and their crystal structures were uncertain. Samples were characterized by optical microscopy, SEM/EDX, powder XRD and DTA. Our results show the existence of a continuous single phase field (γ) ranging from 11.4 to 56.9 at.% Te at 520 °C. A comparison of all obtained diffraction patterns showed clear evidence for a continuously modulated crystal structure. It was possible to refine all powder patterns by applying a structural model in the (3 + 1)-dimensional super-space group R­3m(0,0,γ). Lattice parameters of the basic cell as well as the modulation vector are varying continuously throughout the phase field and the γq-component ({mathbf{q}} = gamma_{q} cdot {mathbf{c}}^{user2{*}}) of the incommensurate q-vector shows a linear extrapolation to pure Sb (γq = 3/2) and Sb2Te3 (γq = 6/5). In agreement with previous authors, the single-phase field γ was found to have a melting point minimum (30 at.% Te, 535 °C). Furthermore, two peritectic reactions were observed and the course of liquidus lines was determined in the whole investigated composition range. The new phase diagram differs considerably from all previous versions, and, for the first time, gives a complete rationalization of the crystal structures observed in the debated composition area.

Highlights from 25 Years of the GeoPT Programme: What Can be Learnt for the Advancement of Geoanalysis

Data submitted over the past 25 years to GeoPT, the highly successful proficiency‐testing programme for the geochemical analysis of geological materials, organised by the International Association of Geoanalysts, provide a valuable resource that permits detailed investigation of contrasting results associated with different sample preparation and measurement principles. Highlighted issues include the following: recurring problems with the dissolution of the refractory minerals zircon and chromite, which produce a large dispersion in data obtained when acid digestion is involved; issues related to different XRF sample preparation methods, whereby a significant divergence of pressed powder pellet results compared with those from fused glass discs is observed; high relative dispersion of data both at low mass fractions, and those higher than normally found in silicate rocks, due to incomplete method validation, in particular due to an overconfidence in estimating reporting limits and to the employment of limited working ranges. In addition, an example for Sr in an ancient pegmatite with extremely high Rb abundance is presented, where ICP‐MS results amount to only to a third of the XRF results, severely underestimated due to the disregard of the radiogenic ingrowth from 87Rb decay. Recommendations are made both for improving data quality and the selection of test materials for future GeoPT rounds.

From machine learning to transfer learning in laser-induced breakdown spectroscopy analysis of rocks for Mars exploration

With the ChemCam instrument, laser-induced breakdown spectroscopy (LIBS) has successively contributed to Mars exploration by determining the elemental compositions of soils, crusts, and rocks. The American Perseverance rover and the Chinese Zhurong rover respectively landed on Mars on February 18 and May 15, 2021, further increase the number of LIBS instruments on Mars. Such an unprecedented situation requires a reinforced research effort on the methods of LIBS spectral data analysis. Although the matrix effects correspond to a general issue in LIBS, they become accentuated in the case of rock analysis for Mars exploration, because of the large variation of rock compositions leading to the chemical matrix effect, and the difference in surface physical properties between laboratory standards (in pressed powder pellet, glass or ceramic) used to establish calibration models and natural rocks encountered on Mars, leading to the physical matrix effect. The chemical matrix effect has been tackled in the ChemCam project with large sets of laboratory standards offering a good representation of various compositions of Mars rocks. The present work more specifically deals with the physical matrix effect which is still lacking a satisfactory solution. The approach consists in introducing transfer learning in LIBS data treatment. For the specific application of total alkali-silica (TAS) classification of rocks (either with a polished surface or in the raw state), the results show a significant improvement in the ability to predict of pellet-based models when trained together with suitable information from rocks in a procedure of transfer learning. The correct TAS classification rate increases from 25% for polished rocks and 33.3% for raw rocks with a machine learning model, to 83.3% with a transfer learning model for both types of rock samples.

Comparation of Pressed Powder Pellet and Fused Glass Bead Preparation Techniques for Mayor Elements Analysis of Rock Samples using X-Ray Fluorescence (XRF)

The composition of chemical elements in rock samples can be used as a tool for classifying rock types, predicting the depositional environment, rock age, and the tectonic environment in which the rock is formed. X-Ray Fluorescence (XRF) is one of the instruments used to analyze rock samples. The advantage of using XRF analysis is that the analysis process can be done more quickly, easily, accurately, and does not damage the sample. However, before measurements are made using the XRF instrument it needs to be supported by an appropriate sample preparation process. In this study, optimal conditions in the standard (CRM) rock sample preparation of GBW 07105 and JR-1 have been studied. The parameters studied were variations in the composition ratio of Cellulose Mycro Crystalin (CMC) with standard (CRM) samples, namely 1: 4 and 1: 3. The technique of mixing the sample is done by using a mortar grinder and a shaker. Optimization of sample preparation was carried out using pressed powder pellet and fused glass bead techniques. Based on the data obtained from the analysis results the best ratio of binders to standard samples is 1: 3. The pressed powder pellet preparation technique is the best technique in analyzing samples using the X-Ray Fluorescence method. Further studies also need to be carried out to analyze minor elements and traces (REEs).

Gamma-Ray Attenuation Study for the Soils of Bursa, Turkey, in the Energy Range 59.5–1332.5 keV

In this study, the gamma radiation attenuation was experimentally investigated for soil samples with different texture collected from Bursa Province, Turkey. Firstly, physical and chemical properties (e.g., density, particle size distribution, lime content, organic matter and chemical composition) of these soils were determined by several methods. The transmission measurements of soils performed by using Am-241, Cs-137, Co-60 and Na-22 sources and 2 × 2 inch NaI(Tl) scintillation detector were used to calculate shielding parameters, mass attenuation coefficient, half value layer and tenth value layer values, of these samples in form of pressed powder pellets. The values of these important parameters have been found to vary with gamma-ray energy and chemical composition of the studied soil samples. For instance, the mass attenuation coefficients were decreased with increasing gamma-ray energies and, with the increase in contribution of MgO and Na components, caused better absorption. The effect of compression pressure on attenuation coefficient was also investigated, and better absorption was observed for the sample pressed by high value of press force.

Heavy metal concentrations and ecological risk assessment for surface sediment of Da Qaidam Salt Lake in Qaidam Basin, northern Tibetan Plateau

The paper focused on heavy metal (Cr, Cu, Pb, Zn, As, Co, Ni and Mn) concentrations from surface sediment in the southeastern Da Qaidam Salt Lake. Based on the pressed powder pellet method and X-ray fluorescence spectrometry analysis, as well as the enrichment factor, geoaccumulation index and potential ecological risk index, the possible sources and pollution level of heavy metals were studied. The results showed that spatial distributions of heavy metal concentration were indicative of nonuniform characteristics in different zones of Da Qaidam Salt Lake, the average enrichment level of heavy metals followed the decreasing order: EF(As) > EF(Mn) > EF(Cu) > EF(Zn) > EF(Pb) > EF(Cr) > EF(Ni) > EF(Co), and arsenic was the main heavy metal contaminant. In a word, the level of heavy metal pollution in the southeastern Da Qaidam Salt Lake was not strong, but anthropogenic emissions would become the main source of heavy metals along with the frequent and strong human activities in the surrounding region.

Geochemical and magnetic data on anthropogenic ashes from municipal solid waste incineration (MSWI).

This paper reports supplementary information to “Understanding room-temperature magnetic properties of anthropogenic ashes from municipal solid waste incineration to assess potential impacts and resources” [1]. The sample-set is composed of 47 samples of bottom (BA) and fly (FA) ashes from Municipal Solid Waste Incineration (MSWI), including eight magnetic extracts of selected BA and FA materials. The sampling relies on a simple random sampling strategy at four different MSWI sites in Northern Italy [2]. X-Ray Fluorescence (XRF) analysis on pressed powder pellets, microscopic observations on thin sections and stubs, and magnetic analysis were carried out.Various magnetic measurements are presented: the magnetic susceptibility measured at two different frequencies (0.47 and 4.7 kHz); the mass-specific susceptibility of ARM (χARM), expressed in m3/kg, calculated after mass-normalization and bias DC field correction; experiments for isothermal remanent magnetization (IRM) experimented were also conducted. The latter measurement allowed the calculation of additional parameters, such as the coercivity of remanence (B0cr) and the S-ratio [3]. The IRM acquired in a field of 1.0 T was regarded as the saturation IRM (SIRM). Mass-specific magnetic susceptibility (χ) was calculated by dividing the volume susceptibility by the sample mass. Finally, hysteresis loops and backfield curves at room temperature were measured on selected samples and are available. Data can be reused as groundwork information in future studies on MSWI residues. It would be essential to produce new data on geochemical and magnetic characteristics of MSWI residues to assure good coverage of data for enhanced sustainability of these heterogeneous streams of anthropogenic materials. This combination of methods will contribute to paving the way for quick and reliable resource assessment as well as to promote environmental sustainability.

Major and trace element analyses of igneous rocks and sediments by X-ray fluorescence spectrometry using glass bead and pressed powder pellet

Major and trace element analyses of igneous rocks and sediments by X-ray fluorescence spectrometry using glass bead and pressed powder pellet

Impact of sample preparation methods for characterizing the geochemistry of soils and sediments by portable X‐ray fluorescence

AbstractWe examined the impact of three different sample preparation methods on bulk soil geochemistry data obtained from a hand‐held, portable X‐ray fluorescence (pXRF) spectrometer. We generated data from a soil core recovered from the surface, downward into unaltered loess, and into a buried soil at a site in eastern Iowa. Samples were scanned (i) directly from field‐moist soil cores; (ii) after drying, grinding, and being loosely massed in plastic cups; and (iii) as pressed‐powder pellets. Data derived using these methods were compared with data obtained from a standard benchtop X‐ray fluorescence (XRF) unit. Generally, the results indicated that data from pressed powder pellets often provide the best correlation to benchtop XRF data, although the results were sometimes element or compound specific. Calcium oxide, Fe2O3, and K2O generally provided the strongest correlations between pXRF‐ and XRF‐reported values; SiO2data were more problematic. Field‐moist pXRF scans generally underestimated element concentrations, but the correlations between pXRF and benchtop XRF measurements were greatly improved after applying pXRF‐derived calibration standards. In summary, although element/compound data provided by pXRF showed significant relationships to benchtop XRF data, the results are improved with proper sample preparation (i.e., drying, grinding, pressing) and usually by calibrating the pXRF data against known standards.

A new carbonate-specific quantification procedure for determining elemental concentrations from portable energy-dispersive X-ray fluorescence (PXRF) data

Portable energy-dispersive X-ray fluorescence (PXRF) analyzers are routinely used to generate large elemental datasets in sedimentary strata. These data provide the basis for assessing stratigraphic changes in geochemistry, bulk mineralogy, and paleo-redox conditions. The manufacturer provided procedure used to calculate elemental concentrations from PXRF photon counts that was developed for siliciclastic mudrocks. This quantification is, however, routinely applied to other sedimentary rocks, such as carbonates, which often have very different elemental concentrations and rock textures. The current study reports elemental concentration data from 57 limestone and dolomite rock samples measured by both PXRF and conventional geochemical analyses including inductively coupled plasma-mass spectrometry (ICP-MS), inductively coupled plasma - optical emission spectrometry (ICP-OES), and wavelength-dispersive X-ray fluorescence (WD-XRF). Carbonate samples were subdivided into two groups. The calibration set (N = 43) is used to establish a carbonate-specific PXRF quantification procedure, and to investigate the effects of different sample preparation techniques. The validation set (N = 14) is used to evaluate the applicability of both the newly developed carbonate-specific quantification procedure and the existing mudrock quantification procedure for the carbonate rock suite.PXRF measured photon counts in the calibration set exhibit strong positive linear correlations (R2 = 1–0.76) with the elemental concentrations independently measured from ICP-MS and/or ICP-OES, and WD-XRF. These linear relationships were used to calculate elemental concentrations in the validation set, which were then statistically compared with the measured elemental concentrations. Results of the carbonate-specific quantification procedure show that 13 elements (Mg, Al, Si, P, K, Ca, Ti, Mn, Fe, Rb, Sr, Y, and Zr) in the carbonate validation set are quantified with PXRF at the definitive data quality level. The mudrock-based quantification procedure, in contrast, quantified only 4 elements at the definite data quality level (Si, K, Ca, and Zr), suggesting that carbonate-specific calibration should be used to ensure higher data quality. The results from the sample preparation experiments exhibit different linear regressions for whole rock, loose powders, pressed powder pellets, and fused discs.The results of this study show that (i) PXRF can reliably identify and accurately quantify the concentrations of 13 common rock-forming elements in carbonate rocks; (ii) the carbonate-specific quantification procedure provides a higher level of data quality for carbonate rocks compared to the mudrock-based quantification; (iii) carbonate rock samples are inherently heterogeneous and thus require more intensive sample preparation and advanced statistical methods to account for this in the quantification procedure; and (iv) the matrix effect that results from different sample preparations must be accounted for in the quantification procedure.

Determination of iron and sulfur valence state in coal ashes by wavelength-dispersive X-ray fluorescence spectrometric technique

This paper describes the technique developed for X-ray fluorescence determination of sulfur and iron valence state in coal concentrates and ashes. The X-ray emission spectra of iron and sulfur were measured using the wavelength-dispersive X-ray fluorescence spectrometer. Samples were prepared as pressed powder pellets on a boric acid substrate. To estimate sulfur valence state SKβ’ satellite was employed. Obtained data show that certified reference material ZUK-2 contains mainly sulfate sulfur and certified reference material KMM-1 contains mainly sulfide sulfur. Results of X-ray fluorescence analysis correspond to certified mineral composition and were proved by the results of certified gravimetric technique analysis. The ratio of divalent and total iron contents was measured using the ratios of FeKβ5 line and FeKβ’ satellite intensities to FeKβ1,3 line intensity. The calibration plots were constructed using certified reference materials of coal concentrates and ashes. The FeO content was determined in CRMs SO-1 (Russia) and CTA-FFA (Poland) for the first time. The accuracy was estimated by comparison with certified titrimetric method results. Using the FeKβ5 and FeKβ1,3 lines intensities ratio allows to quantify ferrous iron.

Unveiling the infrared complex dielectric function of ilmenite CdTiO3

This work presents the infrared active modes of the ilmenite phase of CdTiO3. Since the ilmenite phase of cadmium titanate is unstable in large particle size, the dielectric tensor at the infrared region has been extracted from near normal reflectance of highly reflecting cold pressed powder pellets. The microscopic values of each tensor component were deduced by a new formulation of the effective medium model suitable for anisotropic compacts. This model explicitly takes into account both the matrix and void percolation thresholds, in order to properly determine the dielectric tensor at the region of high frequency longitudinal modes. Both, reflection and absorption experimental data are been confronted with theoretical calculations based on the density functional theory, revealing a great convergence of the values. Additionally, we estimated the quality factor in the microwave region to be: εsx ∼27, εsz ∼20, and Qu × f ∼111,000 GHz (at 10 GHz), enabling the ilmenite CdTiO3 material to be employed as central element in circuitry operating at IEEE X-band.

Thermal diffusivity measurement of ceramic materials used in spraying of TBC systems

The basic goal of this article was thermal diffusivity characterization of ceramic materials used in thermal barrier coating (TBC) systems for depositions of the insulation layer and characterization of the materials’ morphology and remanufacturing process. The base material was oxide 8YSZ (ZrO2 × 8Y2O3), which is usually dedicated to deposition of an insulating top layer in TBC systems. The data related to thermal properties such as thermal diffusivity and thermal conductivity are widely presented in the literature, but there is lack of information about the morphological form of investigated materials, and the presented results vary widely. Data on thermal properties based on the literature sources are inadequate for the real morphological form of materials used in the experiment (e.g., massive or single crystalline material vs. plasma-sprayed coatings), which consequently gives an unsatisfactory accuracy of the obtained numerical simulations by MES methods. This article presents the characterization of thermal diffusivity of the commercial 8YSZ ceramic material synthesized or remanufactured by different routes, which is investigated in the forms of pressed powder pellet (two commercial nano-sized powders with different morphologies), sintered pellets (one commercial powder, solid-state co-precipitated reacted powder of 8YSZ type), and a two-layered coating system of In625 + NiCrAlY/8YSZ type. The range of analysis included morphological investigations of different types of powders in initial conditions and after remanufacturing (sintering, thermal spraying) as well as the thermal diffusivity analysis by the laser flash method. The obtained data were corrected by porosity factor and compared to each other. The best similarity for obtained thermal diffusivity data was found for commercial powers of HOSPTM type after pressing and sintering processes and calculated (2-layered model) value of thermal diffusivity for two-layered system of In625/8YSZ TBS system. The results showed that there are significant differences in thermal diffusivity values for materials with different morphological forms.

Statistically Coherent Calibration of X-Ray Fluorescence Spectrometry for Major Elements in Rocks and Minerals

We applied both the ordinary linear regression (OLR) and the new uncertainty weighted linear regression (UWLR) models for the calibration and comparison of a XRF machine through 59 geochemical reference materials (GRMs) and a procedure blank sample. The mean concentration and uncertainty data for the GRMs used for the calibrations (Supplementary Materials) (available here) filewere achieved from an up-to-date compilation of chemical data and their processing from well-known discordancy and significance tests. The drift-corrected XRF intensity and its uncertainty were determined from mostly duplicate pressed powder pellets. The comparison of the OLR (linear correlation coefficient r∼0.9523–0.9964 and 0.9771–0.9999, respectively, for before and after matrix correction) and UWLR models (r∼0.9772–0.9976 and 0.9970–0.9999, respectively) clearly showed that the latter with generally higher values of r is preferable for routine calibrations of analytical procedures. Both calibrations were successfully applied to rock matrices, and the results were generally consistent with those obtained in other laboratories although the UWLR model showed mostly narrower confidence limits of the mean (slope and intercept) or lower uncertainties than the OLR. Similar sensitivity (∼2.69–46.17 kc·s−1·%−1 for the OLR and ∼2.78–59.69 kc·s−1·%−1 for the UWLR) also indicated that the UWLR could advantageously replace the OLR model. Another novel aspect is that the total uncertainty can be reported for individual chemical data. If the analytical instruments were routinely calibrated from the UWLR model, this action would make the science of geochemistry more quantitative than at present.

High-Temperature-Phase Bi4RhI2: Electronic Localization by Structural Distortion.

The metal-rich compound Bi4RhI2 was discovered in a thorough investigation of the Bi-Rh-I phase system. The monoclinic crystal structure was solved via single-crystal X-ray diffraction. It consists of infinite strands of face-sharing distorted square antiprisms ∞1[RhBi8/2]2+, which are separated by iodide ions. Bi4RhI2 is the high-temperature phase related to the weak three-dimensional topological insulator Bi14Rh3I9 (Bi4.67RhI3) and forms peritectically at 441 °C, where Bi14Rh3I9 decomposes. The structure of Bi4RhI2 is compared with Bi4RuI2 and Bi9Rh2I3, all three sharing a similar intermetallic strand-like structure, although their overall count of valence electrons differs. A chemical bonding analysis of Bi4RhI2 via the electron localizability indicator reveals a complex bonding pattern with covalent bonds between rhodium and bismuth, as well as between bismuth atoms and suggests a possible explanation for the formation of this structure type. Band structure calculations indicate a narrow band gap of 157 meV, which was verified by resistivity measurements on a pressed powder pellet and on single crystals. In a broader context, this strandlike structure type accounts for unusual physical phenomena, such as the transition into a charge-density-wave phase.