Smectite may impact the ability of saline aquifer–caprock systems to store CO2 effectively, because of changes in pressure, temperature, and brine concentration induced by the injection of CO2. These changes influence the molar volume of smectite, affecting the short-term structural and stratigraphic trapping, or the dissolution of smectite via the long-term geochemical trapping. This study investigated the d001 value of an interlayer-cation-exchanged smectite, Na-rich SWy-2 (Na-SWy-2), with Ca or Mg (hereafter CaSWy-2 and MgSWy-2). Molar volume experiments used X-ray diffraction and a high-pressure environmental chamber. The extent of smectite dissolution was simulated at experimental conditions by geochemical modeling using a rate equation derived from the transition state theory. CaSWy-2-CaCl2 and MgSWy-2-MgCl2 brine systems showed that increasing the brine concentration from 0.17 M to saturation results in a <18% decrease in d001 values, and increasing the temperature from approximately 33 to 150°C results in <11% decrease. The effect of the interlayer cation shows the d001 values of MgSWy-2 are <0.4 Å higher compared with CaSWy-2. Geochemical modeling shows the extent of dissolution of Na-SWy-2, CaSWy-2, or MgSWy-2 is only <1.1% in acidic conditions. Furthermore, the calculated swelling pressure needed to decrease the H2O sheets in the interlayer, from 3W to 2W, of MgSWy-2 and CaSWy-2 are higher compared with Na-SWy-2. The swelling pressure was approximated from the sum of the osmotic repulsive pressure, the van der Waals attractive pressure, and the hydration pressure. The data suggest that Na-SWy-2, CaSWy-2, and MgSWy-2 may affect saline aquifer–caprock systems to store CO2. The molar volume is affected by changes in pressure, temperature and brine concentration, or swelling pressure from the injection of CO2. An increase in the d001 value of SWy-2 can enhance the sealing capabilities of a caprock by making saline aquifers less porous and less permeable and thus increasing the capability for CO2 storage. In contrast, a decrease in the d001 value can create cracks in a caprock and thus provide conduits for the CO2 to escape. Furthermore, the CO2 injection will cause a decrease in pH, causing smectite to dissolve until it reaches a steady state. However, despite acidic aquifer conditions, SWy-2 has low solubility.

The dehydration reaction of kerolite was investigated using high-pressure differential thermal analysis at pressures as high as 600 bars. The peak associated with the dehydration is broad, suggesting the presence of a series of overlapping reactions ranging from the release of adsorbed water to interlayer water. The peak temperature is 136°C at 1.8 bars and increases to 516°C at 586 bars. The primary reaction represents loss of adsorbed water having a bond energy of 1.5 ± 1 kJ/mole. A small amount of water may be present as interlayer water and has a bond energy of 7.5 ± 3 kJ/mole.

Twenty-nine chlorites, seventeen lithium-free micas, and twenty-two lithium-bearing micas from diverse localities have been studied by X-ray diffraction, microprobe, and optical second harmonic generation (SHG) techniques to determine which are noncentric and the cause of acentricity. Manandonite (B-rich chlorite) and cookeite, both crystallizing in the Ia form, are acentric. Sudoite-IIb gave a questionable SHG signal, possibly indicating acentricity. All other chlorites gave null signals. Bityite, a Li, Be mica similar to margarite, was determined from the positive SHG response to be acentric. It crystallizes in the 2M1 form and, by analogy to margarite, is ordered tetrahedrally in subgroup symmetry, Cc. Masutomilite-1M and “cryophyllite“-1M (a zinnwaldite high in Al and Si, but low in Fe) are acentric and most probably crystallize in space group C2, thus allowing a noncentric octahedral ordering pattern. Lepidolites showed a diversity in SHG response with only a few being acentric; a lepidolite-1M from Mesagrande, California, a lepidolite-3T from Windhuk, South West Africa, and a lepidolite-2M2 from Nagatare, Japan, gave positive SHG responses. The Japanese material is complexly intergrown and twinned, and intergrain reflection or refraction may have produced spurious signals.

Most lithium-free micas showed diversity in SHG response and, although most were non-emitters, clintonite from Amity, New York, showed a positive response, but this sample is twinned and shows stacking disorder. A “manganophyllite”-1M (manganoan phlogopite) from Langban, Sweden, showed a very weak positive response; however, the presence of Mn alone is not suffcient to produce octahedral cation ordering in noncentric subgroup symmetry. Two manganoan phlogopites from Japan were refined in subgroup symmetry, and the higher order and ideal symmetry of C2/m was confirmed.

Platy (Te Puke, New Zealand), cylindrical (Spruce Pine, North Carolina), and spherical (North Gardiner mine, Huron, Lawrence County, Indiana) halloysite samples were analyzed by high-pressure differential thermal analysis (HP-DTA) to determine the effect of morphological and chemical differences on their respective thermal stability. In halloysite, these morphological differences imply structural features. The metastable phase relations of each are analogous to those of kaolinite. At 1 bar, the platy, cylindrical, and spherical samples showed peak temperatures (maximum deflection in the dehydroxylation endotherm) of 560°, 578°, and 575°C, respectively, whereas at about 600 bars the peak temperatures were 622°, 655°, and 647°C. At low pressures the observed reaction is related to dehydroxylation: halloysite (H) metahalloysite (MH) + vapor (V), whereas higher pressures produce melting reactions, either H + V = metaliquid (ML) for conditions of P(H2O) = P(total), or H + MH = ML for P(H2O) < P(total). The PT conditions of the invariant point, H + MH + ML + V, for each system are: Te Puke, 612° ± 4°C, 25 ± 7 bars; Spruce Pine, 657 ± 2°C, 30 ± 7 bars; North Gardiner, 652° ± 2°C, 34 ± 7 bars. The lower thermal stability of the Te Puke sample may be related to its higher iron content, although additional data are necessary to confirm that it is not related also to the platy structure. Furthermore, morphological differences between the cylindrical and spherical varieties appear to have had little effect on the energy required to dehydroxylate these halloysite structures. Exceptionally high values obtained for the dehydroxylation enthalpies using the van't Hoff equation, compared with values derived using other methods, may be explained by a 10–15-bar excess in the intracrystalline H2O fugacity during dehydroxylation. Intracrystalline fugacity is defined here as the H2O fugacity within crystallites and is not related to the partial pressure of H2O around individual particles.

The dehydration temperature of K-montmorillonite, obtained by ion exchange of a Na-mont-morillonite, was determined at pressures to 2 kbar, using high-pressure differential thermal analysis. Dehydration reactions were found at about 50° and 100°C above the liquid-vapor curve of water. At pressures above the critical point of water the dehydration temperatures increased only slightly. The temperature of the first dehydration reaction is 10°C higher than for Na-montmorillonite, indicating a slightly greater stability of the hydration shell around the potassium interlayer cation. The second dehydration reaction occurs at a slightly lower temperature. The data were used to determine the enthalpy of the dehydration ΔH(dh) and the bonding enthalpy of the interlayer water ΔH(iw) at 1 atm. The first dehydration reaction of the K-exchanged montmorillonite has a ΔH(dh) = 46.16 ± 0.06 kJ/mole and a ΔH(iw) = 7.8 ± 0.5 kJ/mole, whereas for the second reaction, ΔH(dh) = 56.7 ± 2 kJ/mole and ΔH(iw) = 19.8 ± 2 kJ/mole. These values compare with a ΔH(dh) = 46.8 ± 0.3 kJ/mole and a ΔH(iw) = 7.8 ± 0.5 kJ/mole for the first dehydration reaction of the Na-montmorillonite and a ΔH(dh) = 62.9 ± 2 kJ/mole and ΔH(iw) = 27.1 ± 2 kJ/mole for the second dehydration.

Thermal analysis involves a dynamic phenomenological approach to the study of materials by observing the response of these materials to a change in temperature. This approach differs fundamentally from static methods of analysis, such as structural or chemical analyses, which rely on direct observations of a basic property of material (e.g. crystal structure or chemical composition) at a well-defined set of conditions (e.g. temperature, pressure, humidity). Clay minerals are highly susceptible to significant compositional changes in response to subtle changes in conditions. For example, changes in the fugacity of water affect the stability of interlayer H2O in a clay mineral (see below). Therefore, care must be taken that all experimental conditions are known with accuracy and precision

End members and species defined with permissible ranges of composition are presented for the true micas, the brittle micas and the interlayer-cation-deficient micas. The determination of the crystallochemical formula for different available chemical data is outlined, and a system of modifiers and suffixes is given to allow the expression of unusual chemical substitutions or polytypic stacking arrangements. Tables of mica synonyms, varieties, ill-defined materials and a list of names formerly or erroneously used for micas are presented. The Mica Subcommittee was appointed by the Commission on New Minerals and Mineral Names (“Commission”) of the International Mineralogical Association (IMA). The definitions and recommendations presented were approved by the Commission.

Vermiculite crystals from Santa Olalla, Spain, were intercalated with tetramethylammonium (TMA) after Na saturation. The resulting TMA-vermiculite showed near perfect 3-dimensional stacking order with cell parameters of a = 5.353(1) Å, b = 9.273(2) Å, c = 13.616(6) Å, β = 97.68(3)°, and space group C2/m, which indicated a 1M polytype. Single crystal X-ray refinement (R = 0.073, wR = 0.082) located the central atom (N) of the TMA (occupancy at 0.418) and the C atom of 1 methyl group (occupancy at about 0.35). The TMA is offset from the center plane between 2 silicate layers by 1.52 Å, and the methyl group is keyed into the silicate ring of the adjacent silicate layer. This arrangement constrains the positions of the C atoms of the other methyl groups to an opposing plane parallel to the oxygen basal plane. Associated H2O is randomly located between the TMA pillars, and no scattering from these molecules was observed. The calculated height of the TMA molecule is shown to be 4.15 Å.

Steric and electrostatic arguments suggesting that adjacent TMA molecules must alternate apex directions (±c) allow for a description of the local TMA arrangement. This model involves the keying of TMA molecules laterally, thereby explaining why perfect 3-dimensional stacking occurs. The offset of TMA from the center of the interlayer region produces a cavity suitable as an adsorption site for small molecules, such as benzene, which is consistent with the higher than expected adsorption of these molecules in TMA-smectites of high layer charge. This offset also explains the easy expandability of TMA-clays, since only very weak interactions occur between TMA and 1 adjacent silicate layer, thereby allowing molecules to enter the interlayer.

Vermiculite from Santa Olalla, Spain, was intercalated with tetramethylphosphonium [P(CH3)4+ = TMP], using a TMP-bromide solution at 70°C for three weeks. The resulting TMP-exchanged vermiculite, which contained a small (<5% of a site) amount of residual interlayer Ca, showed near perfect three-dimensional stacking. Cell parameters are a = 5.3492(8) Å, b = 9.266(2) Å, c = 14.505(6) Å, β = 97.08(2)°, space group is C2/m, and polytype is lM. Single-crystal X-ray refinement (R = 0.052, wR = 0.061) located two crystallographically unique sites for the phosphorus atoms (TMP molecule). The phosphorus atoms are occupied partially [P1 = 0.146(6), P2 = 0.098(5)] and are offset from the central plane of the interlayer by 1.23 Å to form two P-rich planes in the interlayer. Electrostatic interactions between the P cations and basal oxygen atoms essentially balance the negative charge associated with Al for Si substitutions in the tetrahedral sites. In addition, the orientations of the TMP molecules are probably different owing to packing constraints. The H2O site is located in the center of the interlayer, at the center of the silicate ring, and ∼3.09 Å from the Ca, which is also located on the central plane of the interlayer. Other H2O molecules are present in the interlayer, but could not be located by the diffraction experiment because they are randomly positioned in the interlayer. The tetrahedral rotation angle, α, is affected by the intercalation of TMP relative to tetramethylammonium (TMA), thus indicating that 2:1 layers are not simply rigid substrates, and that dynamic interactions occur during reactions involving adsorption and exchange.

Single-crystal, X-ray examination of Mg,Fe-rich chlorites that were heated at 650°C for 24 hours in air and have undergone dehydroxylation of the interlayer shows that two product phases result with a topotactic relationship, with the c axis of both phases parallel. One phase (“modified chlorite” or “14-A phase”) has relatively sharp reflections with a 14-A c-axis repeat, indicating that it is well crystallized and maintains the 2:1 layer from the parent. Cell parameters are a = 5.368(1)A, b = 9.297(2)A, c = 14.215(6)A, a = 89.86(3)°, ß = 97.15(3)°, γ = 89.98(2)°, and it crystallizes in CĪ symmetry. A structure refinement, details of which will be reported later, indicates that the interlayer consists of two planes, each containing (M + O), where M is the interlayer cation species. These planes show about ±0.5A positional disorder along the [001] direction. There is no evidence for scattering material at z = 0.5 between the 2:1 layers. The second phase in the topotactic relationship is based on a 27-A unit c axis (“27-A phase”). The diffraction data are limited with about 15 diffuse reflections observed, indicating that it is poorly crystallized. The 27-A spacing suggests that both octahedral sheets in the parent chlorite contribute to the formation of this phase.

Heating Mg,Fe-rich chlorite powder in a closed system to 550°C, under either reducing or oxidizing conditions, prevents the formation of the 27-A phase. Because the 27-A phase forms in an open system, we infer that water fugacity is an important factor in its formation. Heating experiments involving samples with different polytypes and octahedral “type” (dioctahedral vs trioctahedral) of the 2:1 layer suggests that these two variables are important. However, the results are equivocal, and an ill-defined B-rich chlorite from Madagascar breaks the observed trends for both variations in stacking sequence and octahedral type. However, B-content may be a factor in the transformation also for those chlorites that contain B.

Vermiculite crystals from Santa Olalla, Spain, were first Na exchanged and then intercalated with monomethylammonium (= NH3(CH3)+, MMA) and dimethylammonium (= NH2(CH3)2+, DMA) molecules, respectively, by immersion in 1 M ammonium-chloride solutions at 65°C for 2–3 wk. MMA-and DMA-exchange with vermiculite resulted in crystals with near perfect three-dimensional stacking, suitable for single crystal X-ray diffraction analysis. Unit cell parameters are: a = 5.353(2) Å, b = 9.273(3) Å, c = 11.950(6) Å, and ß = 98.45(4)° for MMA-exchanged vermiculite and a = 5.351(2) Å, b = 9.268(4) Å, c = 12.423(8) Å, and ß = 98.33(5)° for DMA-exchanged vermiculite. Refinement results are R = 0.059 and wR = 0.073 (MMA-exchanged vermiculite) and R = 0.059 and wR = 0.064 (DMA-exchanged vermiculite). The results are based on structures which show substitutional disorder, and thus the presented models are derived from average structures.

There are two distinct sites for the MMA molecule in MMA-exchanged vermiculite. One crystallo-graphically unique MMA is oriented such that the N-C axis of the molecule is perpendicular to the basal oxygen plane, with the N ion offset from the center of the interlayer by 1.04 Å. The other MMA is located such that the N ion is at the center of the interlayer between adjacent 2:1 layers, presumably with the N-C axis of the molecule oriented parallel to the basal oxygen plane. This represents the first known occurrence of an organic molecule located exactly between the two adjacent 2:1 layers. Both sites are located between hexagonal cavities of adjacent layers. DMA molecules in DMA-exchanged vermiculite are located such that the N ion is offset from the central plane in the interlayer by 0.95 A. A static model is proposed with two orientations of DMA to produce a DMA “zigzag” orientation of molecules parallel to the (001) plane. The plane defined by the C-N-C atoms in the molecule is perpendicular to the (001) plane. An alternate model is more dynamic, and it involves the rotation of DMA molecules about one C-N axis.

Identical starting material was used in previous studies on tetramethylammonium (TMA)-exchanged vermiculite and tetramethylphosphonium (TMP)-exchanged vermiculite. The effect of onium-ion substitutions on the 2:1 layer shows that the tetrahedral rotation angle, α, is significantly smaller for MMA-and DMA-exchanged vermiculite vs. TMA and TMP-exchanged vermiculite. Tetrahedral and octahedral bond distances of the 2:1 layer of the TMA, TMP, MMA, and DMA-exchanged structures may be explained by the location of the organic cation relative to the basal oxygen atom plane and by the differences in the geometries of the organic molecule. Thus, the 2:1 layer is affected by the interlayer molecule, and the 2:1 layer is not a rigid substrate, but interacts significantly with the onium ions.

The objective of this paper is to describe the new serpentine group mineral, guidottiite, which is analogous to cronstedtite. Guidottiite has an ideal chemical composition of (Mn2Fe3+)(SiFe3+)O5(OH)4. The sample is from the N’chwaning 2 mine, Kalahari manganese field, Republic of South Africa, and apparently forms from hydrothermal solutions. Grains are optically near opaque [average index of refraction 1.765, with variable extinction on the (001)], vitreous, and black, with perfect {001} platy cleavage. A non-separable fibrous substructure exists perpendicular to cleavage that results in a silky luster under optical examination. The average chemical analysis determined from electron microprobe based on four grains with ten analyses each resulted in a structural formula of (Mn1.86Fe0.613+Mg0.54)Σ=3.01(Si1.36Fe0.643+)Σ=2.00O5(OH)4, with calculated density of 3.236 g/cm3. Analysis from another area of the sample showed a slightly different chemical composition and resulted in a formula of (Mn1.70Fe0.963+Mg0.24Σ=2.89(Si1.26Fe0.743+)Σ=2.00O5(OH)4, with calculated density of 3.291 g/cm3. The measured density on a bulk sample (with impurities) was 3.33 g/cm3. Thermal analysis suggested a dehydroxylation temperature of 535°C, a decomposition/recrystallization temperature of 722°C, and weight loss (= H2O loss) of 9.4%. The derived Mohs hardness from nano-indentation is H = 4.25.

The sample is mostly the 2H1 polytype with minor amounts of the 2H2 polytype. Using a predominantly 2H2 crystal, which has better crystallinity, the strongest observed X-ray peaks are: 7.21 Å (Io/Io = 100%), 3.543 (50), 2.568 (39), 1.982 (26), and 2.381 (25). All Gandolfi simulations, even with three crystal remountings, showed preferred orientation effects. Transmission electron microscope (TEM) analysis showed stacking disorder within Group D serpentine polytypes. Thus, a regular alternation of the occupancy of octahedral sets within each layer along the stacking exists, but disorder of the layer displacements of 0 and ±b/3 (b defined here as the orthohexagonal cell) exists. Ordered 2H1 (no layer displacement) and 2H2 (alternating + and —b/3 displacement) domains were also frequently observed. X-ray diffraction analysis showed that even apparent single crystals contain impurity phases, presumably Mn-rich and Ca phases that were detected in the microprobe study. The single-crystal structure refinement used a well (stacking) ordered apparent 2H2 crystal with little to no streaking in the diffraction pattern. Results showed that the crystal has a random interstratification of 2H2 and 2H1. The 2H2 polytype is hexagonal, space group P63, with a = 5.5472(3), c = 14.293(2) Å, and Z = 2, and was refined to R1 = 0.072 and wR = 0.108 from 656 unique reflections. Because the two polytypes in the composite have only small differences in the lower 1:1 layer, a large displacement parameter for the basal oxygen atom results, which was constrained to B = 1.5 Å2 (Ueq = 0.0190) in the refinement. Half of the tetrahedral sites in the 2H1 upper layer superpose over half of the tetrahedral sites in the 2H2 upper layer (T1 sites only) per unit cell. This superposition produces an apparent excess of electron densities of the T1 site relative to the T2 site (T1 = 21.9 electrons, T2 = 15.8). Comparison with the microprobe data indicates that observed tetrahedral bond lengths are generally not affected by this intergrowth. Tetrahedral bond lengths indicated that the tetrahedral sites contain T1 = Si0.678 Fe0.3223+ and T2 = Si0.631Fe0.3693+. This excess of electron densities and other refinement problems associated with the guidottiite single-crystal refinement closely parallel all single-crystal cronstedtite-2H2 refinements to date, suggesting that these refinements also involve random interstratifications of 2H2 and 2H1 polytypes.

The structure of trimethylsulfoxonium-exchanged vermiculite has been examined to compare it with other onium-exchanged structures, such as tetramethylammonium- and tetramethylphosphonium-exchanged vermiculite. The three organic cations are tetrahedral in shape, but trimethylsulfoxonium [(CH3)3SO+] has an oxygen atom replacing a methyl group at one apex. This study describes the effect this substitution and the larger S atom have on the site location in the interlayer and the effect on the vermiculite 2:1 layer. These clay minerals may be commercially useful as adsorbents.

Na-exchanged crystals of vermiculite from Santa Olalla, Spain, were intercalated with trimethylsulfoxonium [Me3SO+ = (CH3)3SO+] molecules by refluxing in an aqueous 0.25 M trimethylsulfoxonium iodide solution at 80°C for 14 days. The resulting Me3SO+-exchanged vermiculite crystals were studied by single-crystal, X-ray diffraction methods and by computer modeling (density functional theory). Cell parameters are a = 5.349(2), b = 9.270(3), c = 13.825(8) Å, and β = 97.40(4)°, the space group is C2/m, and the polytype is 1M. Refinement results (R = 0.073, wR = 0.080) show that in the average structure of C2/m, the S atoms of the Me3SO+ molecules form two partially occupied planes [2.066(2) Å from each basal oxygen plane] between the 2:1 layers, and the S atoms show considerable positional disorder. The O atom of the Me3SO+ molecule occurs in the central plane of the interlayer, as far away from each 2:1 layer as possible. In projection down the c* axis, the Me3SO+ molecule resides within the center of the silicate rings from each adjacent 2:1 layer. In the ideal (static) model of the Me3SO+-exchanged vermiculite structure, the Me3SO+ molecule is oriented such that two methyl groups point toward charge-deficient bridging oxygen atoms of the basal plane; thus, the organic pillars charge compensate the bridging oxygen atoms of the 2:1 layer that are charge deficient. In projection, the oxygen atom of the Me3SO+ molecule projects over a tetrahedron containing Si. Computer modeling showed that if H2O is not included in the model, the Me3SO+ molecule (S and O atoms) is in the center of the interlayer, but with the addition of randomly placed H2O, two partially occupied planes similar to the X-ray derived model are formed.

The geochemistry of minerals in intermediate to deep sedimentary rocks (2–10 km depth) is not known sufficiently well to predict accurately the effect of human activities, such as carbon dioxide sequestration or fracking. To carry out real-time experiments, a high-pressure environmental chamber (HPEC) was constructed for in situ X-ray diffraction (XRD) studies to 1000 bars and to 200°C. In the HPEC, a liquid, e.g. a brine, plus sample in suspension, is pressurized by gas, e.g. CH4 or CO2, or liquid, e.g. supercritical CO2. The unique aspect of this chamber is that the sample + liquid (~2 mL) form a dynamic system, and particles can move freely in the liquid while being illuminated by the X-ray beam. Several HPECs were constructed of Ti alloy, stainless steel, or carbon-fiber polyether ketone to be resistant to corrosion under basic or acidic conditions. These HPECs are compatible with standard transmission-mode diffractometers with sealed-tube X-ray sources (Mo radiation is being used at the University of Illinois at Chicago — UIC) or with brilliant X-ray sources. In addition, to allow long-duration studies or, for example, to study the effect of micro-organisms on these mineral reactions, a large-bore (~25 mL) reaction vessel system was devised that could be examined regularly at appropriate P/T conditions or off-line. Calibration of the HPEC and XRD pattern processing is discussed and illustrated. The potential significance of these devices goes beyond understanding the deep sedimentary environment, because materials and reactions can be studied while using nearly any liquid as an immersion agent. As an example, experimental results are given for the d001 values of montmorillonite clay vs. temperatures to 150°C at P(CO2) = 500 bars in a NaCl-rich brine.

A new ferrous phyllosilicate, meifuite, has been discovered in the Yinachang Fe-Cu-REE (rare-earth element) deposit in China. The structural formula, calculated using averaged electron probe microanalysis (EPMA) results, is K0.72Na0.20(Fe5.56Mg0.31Mn0.13)Σ6.00(Si6.95Al1.04)Σ7.99O18.84(OH)4.84 Cl1.33, with an ideal formula of KFe6(AlSi7)O19(OH)4Cl2. The structure of meifuite has a $P\overline{1}$ space group symmetry, with unit-cell parameters of a = 22.7773(13) Å, b = 9.5553(5) Å, c =14.3282(8) Å, α = 99.258(4)°, β = 136.750(3)°, γ = 89.899(4)°, Z = 2, and V = 2077.9(2) Å3. Meifuite has a strip-modulated 2:1 layer (T–O–T) structure similar to that of minnesotaite. About 1/8 of the tetrahedra in the T sheet are occupied by Al instead of Si, and the interlayer cavities are partially occupied by K and Na. Some of the OH sites in the octahedral sheet in the layer structure are fully or partially substituted by Cl, which is apparently the primary reason for the meifuite structure being more stable than stilpnomelane, the most common ferrous layer silicate mineral found at similar temperature and pressure conditions. An updated, more accurate structure model of minnesotaite is also provided for comparison with the meifuite structure. The mineral is named after Meifu Zhou in honor of his outstanding contributions to the field of economic geology.