Bladed Crystals Research Articles

Plumboperloffite, PbMn2+2Fe3+2(PO4)3(OH)3, a new member of the bjarebyite group from Wiperaminga Hill, South Australia, Australia

AbstractPlumboperloffite, PbMn2+2Fe3+2(PO4)3(OH)3, is a new mineral and member of the bjarebyite group from Wiperaminga Hill West Quarry, Boolcoomatta Reserve, Olary Province, South Australia, Australia. The mineral was found in a single cavity in triplite–barbosalite matrix associated with fluorapatite, phosphosiderite, natrodufrénite and fluorite. The mineral forms intergrowths of subparallel, thin tabular to bladed crystals. Individual crystals are up to 40 μm in length. Plumboperloffite is brownish orange in colour with a vitreous lustre. The mineral has brittle tenacity, an excellent cleavage on {100} and uneven fracture. The calculated density is 4.416 g/cm3. Plumboperloffite is biaxial (+), α = 1.87(1), β = 1.88(1) and γ = 1.89(1) as measured in white light. The measured 2V is 88(1)°. Dispersion is apparently strong, based on extinction colours and the orientation is Y = b. The pleochroism in shades of yellow brown is X < Z < Y. Electron microprobe analysis gave the empirical formula (based on 15 O apfu) (Pb0.92Ca0.04Ba0.01K0.01)Σ0.98(Mn2+1.84Fe2+0.13)Σ1.97(Fe3+1.97Al0.03)Σ2.00(P3.01O11.94)(OH)Σ3.06. Plumboperloffite is monoclinic, space group P21/m with a = 9.1765(18), b = 12.340(3), c = 5.0092(10) Å, β = 101.01(3)°, V = 556.8(2) Å3 and Z = 2. The crystal structure has been refined using X-ray single-crystal data to a final R1 = 0.0207 on the basis of 1417 reflections with Fo > 4σ(Fo). The mineral is isostructural with members of the bjarebyite-group minerals.

Kodamaite, Na3(Ca5Na)6Si16O36(OH)4F2·14−xH2O, x = ∼5, A New Layered Alkali-Alkaline Earth Fluorosilicate-Hydrate and Member of the Gyrolite Supergroup, from Mont Saint-Hilaire, Quebec, Canada: Description, Crystal-Chemical Considerations, and Genetic Implications

Abstract Kodamaite, ideally Na3(Ca5Na)6Si16O36(OH)4F2·14−xH2O, where x = ∼5, is a new mineral discovered at the Poudrette quarry, Mont Saint-Hilaire, Quebec, Canada. It develops in spherulitic aggregates up to ∼2 mm across, comprising thin, platy to bladed crystals, with individual crystals averaging <0.05 × 0.5 mm. Crystals are dominated by the form pinacoid {100} with a lesser {hk0} form and typically range from tan to creamy-yellow to white in color, less often being colorless, light or dark green, or white. Associated minerals include eudialyte-group minerals, aegirine, a clinoamphibole, serandite-group minerals, natrolite, molybdenite, pyrite, fluorite, sodalite, catapleiite, rinkite-group minerals, albite, villiaumite, pyrochlore, fluorapatite, microcline, and erdite. Kodamaite is translucent to transparent and has a silky to slightly vitreous luster, a white streak, a Mohs hardness of ∼2, a perfect {001} cleavage, a sectile tenacity, and a smooth fracture. The mineral shows a pronounced bluish-white fluorescence under both long- and medium-wave ultraviolet radiation, much less so under short-wave radiation. The calculated density is 2.16 g/cm3. Optically, kodamaite is presumed to be optically biaxial, but its optical properties could not be readily discerned. An average nD = 1.507 (for λ = 590 nm) was calculated using data from the refined crystal structure. It is non-pleochroic, has low birefringence (first-order gray) and crystals are length slow and show no dispersion. The Raman spectrum shows two strong peaks at 607 (O–Si–O stretch) and 1070 cm−1 (Si–O stretch), along with several weaker ones over the range of ∼100–500 cm−1 arising from a combination of alkali–O bonds and lattice vibrations. An average of 11 energy-dispersive spectroscopic analyses gave Na2O 8.55, CaO 16.80, Fe2O3 0.39, SiO2 60.76, F 2.57, Cl 0.11, H2O (calc.) 12.49, O=F −1.08, O=Cl −0.02, total 100.98 wt.%. The empirical formula [based on Σ16(Si+S6+) cations apfu] is Na3.14(Ca4.72Na1.30Fe0.08)Σ6.00(Si15.92S6+0.08)Σ16O36.09(OH3.82F0.13Cl0.08)Σ4.00F2·9H2O. The crystal-structure formula is NaNa2Ca2Ca2(NaCa)2Si16O36(OH)4F2·14−xH2O with x = ∼5, which may be simplified to Na3(Ca5Na)6Si16O36(OH)4F2·9H2O. The mineral is triclinic, crystallizing in space group P, with a = 9.609(2), b = 9.630(2), c = 15.739(3) Å, α = 75.21(3), β = 85.22(3), γ = 60.12(3) °, V = 1219.3(1) Å3, Z = 1. The strongest six lines of the X-ray powder-diffraction pattern [dobs in Å (Iobs) (hkl)] are: 15.197 (100) (001), 3.833 (7) (004), 3.068 (7) (005), 2.996 (18) , 2.780 (14) , 1.831 (9) . The crystal structure was refined to R = 8.43%, wR2 = 23.50% using single-crystal X-ray diffraction data (1578 reflections with Fo > 4σFo). Kodamaite has a strongly layered crystal structure, with a motif based on single sheets of SiO4 tetrahedra (T) that are composed of regular, planar, six-membered rings (with a u6 arrangement; apices of the tetrahedra all point in a common direction, up = u). The regular rings of tetrahedra are linked in the (001) plane by SiO3(OH) tetrahedra, whose apical directions are opposite to those in the ring (down; d). Linkages between the two types of tetrahedra give rise to an irregular, six-membered ring of tetrahedra with a u2du2d arrangement. The combination of regular and irregular six-membered rings of tetrahedra produces a three-connected (63)4 net. Two symmetry-related T layers, designated T2 and −T2, sandwich a closest-packed layer of edge-sharing Naφ6 and Caφ6 octahedra and Naφ8 polyhedra (φ = undefined ligand; O, F), forming a quasi-layer of octahedra (O). Refinement of the crystal structure shows the Ca sites are dominated by Ca with small amounts of Na (9:1 ratio); one of the sites has an equal concentration of Ca and Na, suggesting ordering of the two in a single site. The arrangement of T and O layers produces a TOT module with the interlayer space being occupied by H2O groups. Charge-balance arguments and observed anion–anion distances support ordering of F in a single, distinct site. The complete crystal structure of kodamaite conforms to a scheme, which is similar to that of the closely related minerals martinite and ellingsenite. All are classed in the gyrolite supergroup, which includes minerals in five groups, all having similar but distinct crystal-structure features. The crystal-chemical relationships among the groups and implications in terms of the stacking of various modules are presented and discussed. Kodamaite is a late-stage mineral that developed under hydrothermal conditions at T < 200 °C, most likely under high to very high alkalinity. The interaction of these fluids with pre-existing minerals, including pectolite, eudialyte-group minerals, and sodalite, is likely essential to the formation of the kodamaite.

Stanevansite, Mg(C2H3O3)2·2H2O, A New Hydrous Glycolate Mineral, from the Santa Catalina Mountains, Tucson, Arizona, USA

Abstract A new organic mineral species, stanevansite, ideally Mg(C2H3O3)2·2H2O, was discovered from the western end of Pusch Ridge in the Santa Catalina Mountains (32° 21′ 42″ N, 110° 57′ 30″ W, at the elevation of 975 m), north of Tucson, Arizona, USA. It occurs as sprays of bladed crystals (up to 0.40 × 0.07 × 0.03 mm). Associated minerals include lazaraskeite, chrysocolla, malachite, wulfenite, mimetite, phosphohedyphane, cerussite, hematite, calcite, microcline, phlogopite, and quartz. Stanevansite crystals are colorless in transmitted light, transparent with white streak and vitreous luster. They are brittle and have a Mohs hardness of ∼1½; cleavage is perfect on {100}. Twinning is common on (100). The measured and calculated densities are 1.69(5) and 1.682 g/cm3, respectively. Optically, stanevansite is biaxial (+), with α = 1.539(5), β = 1.545(5), γ = 1.558(5), 2Vmeas. = 62(2)°, 2Vcal. = 69°. It is insoluble in water, but slowly dissolves in hydrochloric acid. An electron-microprobe analysis yielded an empirical formula, based on 8 O apfu and Σ(Mg + Zn) = 1 apfu, of (Mg0.95Zn0.05)Σ1.00(C2H3O3)2·2H2O, which can be simplified as (Mg,Zn)(C2H3O3)2·2H2O. Stanevansite is monoclinic with space group P21/c and unit-cell parameters a = 11.4927(2), b = 5.85470(10), c = 12.4711(2) Å, β = 91.1610(10)°, V = 838.96(2) Å3, and Z = 4. It is isostructural with several synthetic glycolate compounds having the general chemical formula M2+(C2H3O3)2·2H2O, where M2+ = Co2+, Mn, Zn, and Mg. The crystal structure of stanevansite is characterized by the mononuclear complex [Mg(C2H3O3)2(H2O)2], with such complexes being connected to one another by hydrogen bonds to form a three-dimensional supramolecular architecture. In a [Mg(C2H3O3)2(H2O)2] complex, Mg is octahedrally coordinated by two chelating glycolate ligands and two H2O molecules. Stanevansite represents the first hydrous glycolate mineral and is believed to have formed through the interaction of fluids containing glycolic acid (C2H4O3) derived from decaying plant materials or bacterial activities with Mg produced by the alteration of primary and secondary minerals. Its discovery, together with other glycolate minerals documented recently, namely lazaraskeite Cu(C2H3O3)2, jimkrieghite Ca(C2H3O3)2, and lianbinite (NH4)(C2H3O3)(C2H4O3), not only implies that more glycolate minerals may be found in nature, but also suggests that glycolate minerals may serve as a potential reservoir for biologically fixed carbon.

Tamarugite, NaAl(SO4)2·6H2O, as a valuable indicator of soil degradation in a Spanish coastal wetland receiving acidic leachates from spilled mine waste

This paper documents the first occurrence of tamarugite in a Spanish coastal wetland registered as a UNESCO Biosphere Reserve, and discusses its origin and environmental significance. Tamarugite occurs as bladed crystals in efflorescent coatings on the topsoil of marshy areas, alongside an abandoned mining railroad. Tamarugite formation is described as a sequential process involving: (1) Oxidative dissolution of pyrite ore spilled on the former railway tracks and generation of acidic sulfate-rich waters; (2) decomposition of layer minerals under acidic conditions and release of Al3+ ions into solution; (3) interaction between acid discharges and estuarine water during flood tidal periods; and (4) precipitation of tamarugite and associated sulfate salts (sideronatrite, epsomite, pickeringite) under strongly evaporative conditions. These transient minerals have potential to release acid and associated major elements (Al, Fe, Mg, Na, S) and trace metals (e.g. Zn) into the solution causing detrimental effects. The occurrence of tamarugite is, therefore, a valuable indicator of environmental degradation in wetland ecosystems.

Nickelalumite, ideally NiAl4(SO4)(OH)12(H2O)3, a new-old mineral from the Kara-Tangi uranium deposit, Kyrgyzstan

Nickelalumite, ideally NiAl4(SO4)(OH)12(H2O)3, is a newly approved mineral from the Batken region, Kyrgyzstan, where it occurs in the Kara-Tangi and Kara-Chagyr uranium deposits. It formed in a zone of hydrothermal alteration of U–V-bearing carbonaceous siliceous schists, in association with quartz, calcite, alumohydrocalcite, allophane, crandallite, kyrgyzstanite, ankinovichite and an unknown Al–OH-mineral. It occurs as aggregates of colourless to pistachio-green radiating bladed crystals from 0.05 to 0.50 mm long. It is vitreous to transparent in thin flakes, has a white streak, and shows no fluorescence under long-wave or short-wave ultraviolet light. Cleavage is perfect parallel to {001} and no parting was observed. Mohs hardness is 2, it is brittle and has a splintery fracture. The calculated mass density is 2.231 g cm–3. In transmitted plane-polarized white light, nickelalumite is non-pleochroic, biaxial, α = 1.542(2), γ = 1.533(2), β could not be measured due to the almost negligible thickness of the flakes. EPMA chemical analysis gave Al2O3 39.94, SiO2 0.17, SO3 15.20, V2O3 0.29, FeO 0.15, NiO 8.00, ZnO 6.21, (H2O)calc. 31.87, total 101.83 wt%, H2O was determined by crystal-structure analysis, and the empirical formula is as follows: (Ni0.55Zn0.39V0.02Fe0.01)Σ0.97(Al3.99Si0.01)Σ4.00 (SO4)(OH)12(H2O)3 based on 4 (Al + Si) cations. There is considerable variation in substitution of Zn, Cu, Fe and V3+ for Ni and V5+ for S6+. Nickelalumite is monoclinic, P21/n, a = 10.2567(5), b = 8.8815(4), c = 17.0989(8) Å, β = 95.548(1)°, V = 1550.3(2) Å3, Z = 4. The crystal structure of nickelalumite was refined to an R1 index of 5.66% and consists of interrupted [NiAl4(OH)12] sheets intercalated with layers of {(SO4)2(H2O)3}; nickelalumite is a member of the chalcoalumite group.

Bernardevansite, Al2(Se4+O3)3⋅6H2O, dimorphous with alfredopetrovite and the Al-analogue of mandarinoite, from the El Dragón mine, Potosí, Bolivia

AbstractA new mineral species, bernardevansite (IMA2022-057), ideally Al2(Se4+O3)3⋅6H2O, has been discovered from the El Dragón mine, Potosí Department, Bolivia. It occurs as aggregates or spheres of radiating bladed crystals on a matrix consisting of Co-bearing krut'aite–penroseite. Associated minerals are Co-bearing krut'aite–penroseite, chalcomenite and ‘clinochalcomenite’. Bernardevansite is colourless in transmitted light, transparent with white streak and vitreous lustre. It is brittle and has a Mohs hardness of 2½–3. Cleavage is not observed. The measured and calculated densities are 2.93(5) and 2.997 g/cm3, respectively. Optically, bernardevansite is biaxial (+), with α = 1.642(5), β = 1.686(5) and γ = 1.74(1) (white light). An electron microprobe analysis yielded an empirical formula (based on 15 O apfu) (Al1.26Fe3+0.82)Σ2.08(Se0.98O3)3⋅6H2O, which can be simplified to (Al,Fe3+)2(SeO3)3⋅6H2O.Bernardevansite is the Al-analogue of mandarinoite, Fe3+2(SeO3)3⋅6H2O or dimorphous with P$\bar{6}$2c alfredopetrovite. It is monoclinic, with space group P21/c and unit-cell parameters a = 16.5016(5), b = 7.7703(2), c = 9.8524(3) Å, β = 98.258(3)°, V = 1250.21(6) Å3 and Z = 4. The crystal structure of bernardevansite consists of a corner-sharing framework of M3+O6 (M = Al and Fe) octahedra and Se4+O3 trigonal pyramids, leaving large voids occupied by the H2O groups. There are two unique M3+ positions: M1 is octahedrally coordinated by (4O + 2H2O) and M2 by (5O + H2O). The structure refinement indicates that Al preferentially occupies M1 (= 0.692Al + 0.308Fe) over M2 (= 0.516Al + 0.484Fe). The substitution of the majority of Fe in mandarinoite by Al results in a significant reduction in its unit-cell volume from 1313.4 Å3 to 1250.21(6) Å3 for bernardevansite. The discovery of bernardevansite begs the question whether the Fe3+ end-member, Fe3+2(SeO3)3⋅6H2O, has two polymorphs as well, one with P21/c symmetry, as for mandarinoite and the other P$\bar{6}$2c, as for alfredopetrovite.

Loomisite, Ba[Be2P2O8]⋅H2O, the first natural example with the zeolite ABW-type framework, from Keystone, Pennington County, South Dakota, USA

AbstractA new beryllophosphate mineral species, loomisite (IMA2022-003), ideally Ba[Be2P2O8]⋅H2O, was found from the Big Chief mine near Keystone, Pennington County, South Dakota, USA. It occurs as divergent sprays of very thin bladed crystals with a tapered termination. Individual crystals are found up to 0.80 × 0.06 × 0.03 mm. Associated minerals include dondoellite, earlshannonite, mitridatite, rockbridgeite, jahnsite-(CaMnFe) and quartz. No twinning or parting is observed macroscopically. Loomisite is murky white in transmitted light, transparent with white streak and silky to vitreous lustre. It is brittle and has a Mohs hardness of 3½–4, with perfect cleavage on {100} and {$\bar{1}$10}. The measured and calculated densities are 3.46(5) and 3.512 g/cm3, respectively. Optically, loomisite is biaxial (+), with α = 1.579(5), β = 1.591(5), γ = 1.606(5) (white light), 2V (meas.) = 82(2)° and 2V (calc.) = 85°. It is non-pleochroic under polarised light, with a very weak (r > v) dispersion. The mineral is insoluble in water or hydrochloric acid. An electron microprobe analysis, along with the BeO content measured with an ICP-MS, yields an empirical formula (based on 9 O apfu) (Ba0.96Ca0.06)Σ1.02[(Be1.96Fe0.06)Σ2.02P1.99O8]⋅H2O, which can be simplified to (Ba,Ca)[(Be,Fe)2P2O8]⋅H2O.Loomisite is monoclinic, with space group Pn and unit-cell parameters a = 7.6292(18), b = 9.429(2), c = 4.7621(11) Å, β = 91.272(5)°, V= 342.47(14) Å3 and Z = 2. Its crystal structure is characterised by a framework of corner-sharing PO4 and BeO4 tetrahedra. The framework can be considered as built from the stacking of sheets consisting of 4- and 8-membered rings (4.82 nets) along [001] or hexagonal layers (63 nets) along [010]. The extra-framework Ba2+ and H2O are situated in the channels formed by the 8-membered rings. Topologically, loomisite represents the first natural example with the zeolite ABW-type framework, which is adopted by over 100 synthetic compounds with different chemical compositions.

Lauraniite, Cu6Cd2(SO4)2(OH)12·5H2O, a New Copper Cadmium Sulfate Mineral from the Laurani Mine, Bolivia

ABSTRACT Lauraniite, Cu6Cd2(SO4)2(OH)12·5H2O, is a new mineral from the Laurani Mine, Aroma Province, La Paz Department, Bolivia, where it is found as a secondary mineral associated with serpierite and brochantite, on a matrix consisting of tennantite and chalcocite. Lauraniite occurs as bladed crystals up to 110 μm in length. Crystals are pale blue and transparent, with a vitreous luster and a white streak. Fracture is uneven. Cleavage is perfect on {100}. The calculated density is 3.40 g/cm3 based on the empirical formula. Optically, lauraniite is uniaxial (+) with α = 1.637(3), β = 1.638(3), γ = 1.638(3) (white light), 2V = 20(2)°, and orientation Z ≈ a. The empirical formula, based on data obtained from electron microprobe analysis, is Cu6.13(Cd1.62Zn0.24)(SO4)1.96(OH12.03Cl0.05)12.08·5.08H2O. Lauraniite is monoclinic, P21/c, a = 7.3200(15), b = 25.424(5), c = 11.283(2) Å, β = 91.62(3)°, V = 2099.0(7) Å3, and Z = 4. The crystal structure, determined using single-crystal data obtained using synchrotron radiation, refined to R1 = 0.0468% for 5999 observed reflections with Fo > 4σ(Fo). It is characterized by undulating, brucite-like sheets consisting of seven Cuϕ6 (ϕ: O2–, OH–, H2O) octahedra and two Cd(OH)6(H2O) polyhedra. Sheets are decorated on one side by corner-sharing SO4 tetrahedra. Linkages between adjacent sheets are provided by H-bonds.

Dondoellite, Ca2Fe(PO4)2·2H2O, a New Mineral Species Polymorphic with Messelite, from Rapid Creek, Yukon, Canada

ABSTRACT A new mineral species, dondoellite, ideally Ca2Fe(PO4)2·2H2O, was found in the Grizzly Bear Creek, Dawson mining district, Yukon, Canada. It is polymorphic with messelite, a member of the fairfieldite group. Dondoellite occurs as spherical aggregates (diameters up to 2 cm) of radiating bladed crystals. Associated minerals include hydroxylapatite, siderite, and quartz. No twinning or parting is observed. The mineral is colorless to pale yellow in transmitted light, is transparent with white streak, and has vitreous luster. It is brittle and has a Mohs hardness of 3½–4, with perfect cleavage on {001}. The measured and calculated densities are 3.14(5) and 3.15 g/cm3, respectively. Optically, dondoellite is biaxial (+), with α = 1.649(5), β = 1.654(5), γ = 1.672(5) (white light), 2V (meas.) = 55(2)°, 2V (calc.) = 58°. An electron probe microanalysis yields an empirical formula (based on 10 O apfu) Ca1.99(Fe0.89Mg0.13Mn0.01)Σ1.03(P1.00O4)2·2H2O, which can be simplified to Ca2(Fe2+,Mg,Mn2+)(PO4)2·2H2O. Dondoellite is triclinic, space group P, a = 5.4830(2), b = 5.7431(2), c = 13.0107(5) Å, α = 98.772(2), β = 96.209(2), γ = 108.452(2)°, V = 378.71(2) Å3, and Z = 2. The crystal structure of dondoellite is characterized by isolated FeO4(H2O)2 octahedra that are linked by corner-sharing with PO4 tetrahedra to form so-called kröhnkite-type [Fe(PO4)2(H2O)2]2– chains along [100], similar to that observed in messelite. These chains are connected to one another by large Ca2+ cations and H bonds to form layers parallel to (001). The layers are further linked together by Ca–O and H bonds. However, unlike messelite, the crystal structure of dondoellite contains two symmetrically independent PO4 tetrahedra (P1O4 and P2O4) and two distinct CaO7(H2O) polyhedra (Ca1 and Ca2). The kröhnkite-type chains in dondoellite are constructed with P1O4 tetrahedra on one side and P2O4 tetrahedra on the other. Topologically, the dondoellite structure can be considered a combination of the collinsite and messelite structures alternating along [001], thus representing a new structure type for minerals with kröhnkite-type chains. The discovery of dondoellite raises the question as to whether polymorphs of fairfieldite, Ca2Mn2+(PO4)2·2H2O, or collinsite, Ca2Mg(PO4)2·2H2O, might also be found in nature.

Nitroplumbite, [Pb4(OH)4](NO3)4, a New Mineral with Cubane-Like [Pb4(OH)4]4+ Clusters from the Burro Mine, San Miguel County, Colorado, USA

ABSTRACT Nitroplumbite (IMA2021-045a), [Pb4(OH)4](NO3)4, is a new mineral discovered at the Burro mine, Slick Rock district, San Miguel County, Colorado, USA. It occurs in a secondary efflorescent assemblage on asphaltite and montroseite- and corvusite-bearing sandstone in association with baryte, chalcomenite, and volborthite. The mineral forms as brown equant (pseudocubic) or colorless bladed crystals. The streak is white, luster is vitreous to greasy, Mohs hardness is 2½, tenacity is brittle, and fracture is conchoidal. Nitroplumbite is optically biaxial (–) with α = 1.790(5), β =1.820 (est.), and γ = 1.823 (est.) (white light); 2Vmeas = 35(1)°; optical orientation: Z = b; nonpleochroic. The calculated density is 5.297 g/cm3 for the empirical formula. Electron probe microanalysis provided the empirical formula Pb4.18(OH)4(N0.98O3)4. Nitroplumbite is monoclinic, space group Ia, a = 18.3471(7), b = 17.3057(4), c = 18.6698(8) Å, β = 91.872(3)°, V = 5924.7(4) Å3, and Z = 16. The crystal structure (R1 = 0.0509 for 11161 I > 2σI reflections) is the same as that previously determined for its synthetic analogue. It consists of isolated, internally bonded cubane-like [Pb4(OH)4]4+ clusters and isolated (NO3)– groups that are linked together by long Pb–O bonds and hydrogen bonds.

Gurzhiite, Al(UO2)(SO4)2F⋅10H2O, a new uranyl sulfate mineral with a chain structure from the Bykogorskoe deposit, Northern Caucasus, Russia

AbstractGurzhiite, ideally Al(UO2)(SO4)2F⋅10H2O, is a new uranyl sulfate mineral from the Bykogorskoe U deposit, Northern Caucasus, Russia. It occurs as fine-grained aggregates forming veinlets up to 50 cm long in cracks of the brecciated rock. Gurzhiite aggregates are composed of small bladed crystals up to 0.1 mm across. Associated minerals include khademite and quartz. Gurzhiite is pale yellow in crystals, lemon yellow in aggregates, transparent with a vitreous lustre and a white streak. It is brittle and has an irregular fracture. Cleavage is good on {001}. The new mineral exhibits a bright yellow–green fluorescence under both longwave and shortwave UV radiation. Mohs hardness is ~2. Dmeas = 2.52(3) g/cm3 and Dcalc = 2.605 g/cm3. The mineral is biaxial (–) with α = 1.528(3), β = 1.538(2), γ = 1.544(3) (589 nm); 2Vmeas= 80(10)° and 2Vcalc = 75.1°. The empirical formula calculated on the basis of 21(O + F) atoms per formula unit (apfu) is Al0.92Zn0.05Fe3+0.03Na0.03U0.95S2.00O9.85F0.99⋅10.16H2O. Gurzhiite is triclinic, with space group P$\bar{1}$, a = 7.193(2), b = 11.760(2), c = 11.792(2) Å, α = 67.20(3), β = 107.76(3), γ = 89.99(3)°, V = 867.7(4) Å3 and Z = 2. The five strongest lines of the powder X-ray diffraction pattern [d, Å (I, %)(hkl)] are: 10.24(100)(001); 5.40(14)($\bar{ 1}\bar{1}$1); 5.11(54)(002); 3.405(11)($\bar{2}$11); and 3.065(11)($\bar{1}\bar{1}$3). The crystal structure of gurzhiite is based upon uranyl sulfate chains of the same type as in bobcookite and svornostite. Between the chains are two types of Al-octahedra – Al1(H2O)6 and Al2F2(H2O)4. The entire structure stability is maintained by a complex network of H bonds. The new mineral honours Russian mineralogist and crystallographer Dr. Vladislav V. Gurzhiy in recognition for his contributions to uranium mineralogy and crystallography.

The first occurrence of the carbide anion, C4–, in an oxide mineral: Mikecoxite, ideally (CHg4)OCl2, from the McDermitt open-pit mine, Humboldt County, Nevada, U.S.A.

AbstractMikecoxite, ideally (CHg4)OCl2, is the first mercury-oxide-chloride-carbide containing a C4– anion coordinated by four Hg atoms (a permercurated methane derivative) to be described as a mineral species. It was found at the McDermitt open-pit mine on the eastern margin of the McDermitt Caldera, Humboldt County, Nevada, U.S.A. It is monoclinic, space group P21/n, Z = 4; a = 10.164(5), b = 10.490(4), c = 6.547(3) Å, V 698.0(5) Å3. Chemical analysis by electron microprobe gave Hg 86.38, Cl 11.58, Br 0.46, C 1.81, sum = 100.23 wt%, and O was detected but the signal was too weak for quantitative chemical analysis. The empirical formula, calculated on the basis of Hg + Cl + Br = 6 apfu, is (C1.19Hg3.39)(Cl2.57Br0.05)Σ2.62, and the ideal formula based on the chemical analysis and the crystal structure is (CHg4)OCl2. The seven strongest lines in the X-ray powder diffraction pattern are [d (Å), I, (hkl)]: 2.884, 100, (230); 2.989, 81, (301, 301, 112, 112, 131, 131); 2.673, 79, (122, 122, 212, 212); 1.7443, 40, (060, 432, 432); 5.49, 34, (101, 101); 4.65, 32, (120); 2.300, 30, (312, 312). The Raman spectrum shows three bands at 638, 675, and 704 cm–1, well above the range characteristic of NHg4 stretching vibrations between 540 and 580 cm–1, that are assigned to CHg4 stretching vibrations. Mikecoxite forms intergrowths of bladed crystals up to 100 μm long that occur on granular quartz or in vugs associated with kleinite. It is black with a submetallic to metallic luster and strong specular reflections and does not fluoresce under short-or long-wave ultraviolet light. Neither cleavage nor parting were observed, and the calculated density is 8.58 g/cm3. In the crystal structure of mikecoxite, (C4–Hg42+) groups link through O2– ions to form three-membered rings that polymerize into corrugated [CHg4OCl]+ layers with near-linear C4––Hg2+–O and C 4––Hg2+–Cl linkages. The layers link in the third direction directly via weak Hg2+–O2– and Hg2+–Cl– bonds to adjacent layers and also indirectly via interlayer Cl–. A bond-valence parameter has been derived for (Hg2+–C4–) bonds: Ro = 2.073 Å, b = 0.37, which gives bond-valence sums at the C4– ions in accord with the valence-sum rule. The source of carbon for mikecoxite in the volcanic high-desert environment of the type locality seems to be methane, with the reaction catalyzed by microbiota through full mercuration of carbon atoms, beyond the first stage that produces the volatile and highly mobile methylmercury, [CH3Hg]+, a potent neurotoxin that accumulates in marine food chains. Both the mineral and the mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2021-060). The mineral is named after Michael F. Cox (b. 1958), a founding member of the New Almaden Quicksilver County Park Association (NAQCPA) who was responsible for characterizing and remediating environmental mercury on-site and who recovered the rock containing the new mineral.

Diagenetic Barite-Pyrite-Wurtzite Formation and Redox Signatures in Triassic Mudstone, Brooks Range, Northern Alaska

Mineralogical and geochemical studies of interbedded black and gray mudstones in the Triassic part of the Triassic-Jurassic Otuk Formation (northern Alaska) document locally abundant barite and pyrite plus diverse redox signatures. These strata, deposited in an outer shelf setting at paleolatitudes of ~45 to 60°N, show widespread sedimentological evidence for bioturbation. Barite occurs preferentially in black mudstones (TOC = 0.93–6.46 wt%), forming displacive euhedral crystals with pyrite inclusions and rims, and late albite inclusions or intergrowths. Pyrite also occurs as small (3–20 μm) framboids, discontinuous laminae, euhedral and anhedral crystals, and replacements of barite and fossils (mainly radiolarians). Paragenetically early wurtzite is present as clusters of very small (1–3 μm) aggregates of radiating crystals 0.5 to 1.0 μm long with cores of organic matter that overgrow framboidal pyrite; later wurtzite forms 10- to 30-μm bladed crystals. Equant grains (3–30 μm) and small (20 μm) angular clusters of zinc sulfide that include <1-μm-long, comb-like structures are sphalerite or wurtzite, or both. Minor siderite forms euhedral crystals intergrown with albite that enclose wurtzite and barite. Illite shows intergrowths with sphalerite; rare K-feldspar is intergrown with barite. Formation of these minerals and assemblages is attributed to early diagenetic processes.Whole-rock geochemical data for 15 samples show large ranges in redox proxies including Post Archean Average Shale (PAAS)-normalized enrichment factors (EFs) for V, U, Mo, and Re, and Al-normalized ratios for V, U, and Mo. Results for most black mudstones, with or without abundant barite and/or pyrite, suggest deposition within an oxygen minimum zone. Cerium anomalies, PAAS-normalized and calculated on a detrital-free basis, range widely from 0.49 to 0.96 and may reflect diagenetic overprinting by Ce-depleted fluids. Considering data for both black and gray mudstones, the overall geochemical pattern together with evidence from pyrite framboid sizes suggest that redox conditions fluctuated greatly from euxinic to oxic, like the redox profiles reported for modern shelf sediments offshore Peru and Namibia. The euxinic redox signatures in some Otuk black mudstones may correlate with widespread Early to Middle Triassic ocean anoxic events proposed for other regions.Calculations of median EFs for trace elements in Otuk black mudstones reveal both enrichments and depletions. Normalizations to the median composition of the three least-mineralized black mudstones show that barite- and/or pyrite-rich samples display large (>50%) positive changes for Li (+80.4%), V (+75.6%), Sr (+75.9%), Ba (+790%), Cu (+92.1%), Ni (+169%), Ag (+156%), Au (+3091%), As (+109%), Sb (+476%), and Se (+205%); Zn shows a moderate positive change of +42.1%. Moderate negative changes are evident only for Ge (−47.2%) and W (−30.6%). The local enrichments may reflect one or more factors including redox variations in bottom waters and pore fluids, element mobility during diagenesis, and selective fractionation into minerals such as barite, pyrite, and wurtzite. Anomalously low U/Al and UEF values, compared to those for other modern and ancient organic-rich sediments and sedimentary rocks, are attributed to increased solubility and loss of U during bioturbation-related oxygenation in the subsurface.Physicochemical constraints on barite, pyrite, and wurtzite formation are informed by use of a pH-fO2 plot constructed at 10 °C. Based on paragenetic evidence for multistage deposition of these three minerals, together with the presence of illite intergrown with ZnS and K-feldspar with barite, proposed diagenetic trends involve an increase in pH and fO2 related to the ingress of sulfate-rich pore fluids during bioturbation, followed by a return to lower then higher pH and fO2 conditions linked to carbon, sulfur, barium, and iron cycling during diagenesis. Labile Ba of marine pelagic origin was mobilized from organic-rich sediment upward to the sulfate-methane transition zone where barite precipitated during the interaction of reduced Ba- and CH4-rich fluids with sulfate-bearing pore fluids. The formation of paragenetically early wurtzite (ZnS) crystals, as well as locally high EF values for Cu, Ni, Ag, and Au, is attributed to metal enrichment of pore fluids, with sources being derived in part from water-column deposition from hydrothermal plumes related to coeval Triassic seafloor vent systems including a volcanogenic massive sulfide deposit in British Columbia and the Wrangellia Large Igneous Province in Alaska.

Beachrock as a Paleoshoreline Indicator: Example from Wadi Al-Hamd, South Al-Wajh, Saudi Arabia

The present study concerns the Holocene inland beachrocks that are exposed in the Red Sea coastal plain at the mouth of Wadi Al-Hamd, South Al-Wajh City, Saudi Arabia, and their utility as an indicator for Holocene climate and sea level changes. In addition, the framework composition, and carbon and oxygen isotopic data, are employed to interpret the origin of their cement. The beachrock consists mainly of gravel and coarse-grained terrigenous sediments dominated by lithic fragments of volcanic rocks, cherts and rare limestones along with quartz, feldspars and traces of amphiboles and heavy minerals. In addition, rare skeletal remains dominated by coralline algae, benthic foraminifera and mollusca remains are recognized. The allochems are cemented by high Mg-calcite (HMC) formed mainly in the intertidal zone under active marine phreatic conditions. The cement takes the form of isopachous to anisopachous rinds of bladed crystals, micritic rim non-selectively surrounding siliciclastic and skeletal remains, and pore-filling micrite. Pore-filling micrite cement occasionally displays a meniscus fabric, suggesting a vadose environment. The δ18O and δ13C values of carbonate cement range from −0.35‰ to 1‰ (mean 0.25‰) and −0.09‰ to 3.03‰ (mean 1.85‰), respectively, which are compatible with precipitation from marine waters. The slight depletion in δ18O and δ13C values in the proximal sample may suggest a slight meteoric contribution.

Lazaraskeite, Cu(C2H3O3)2, the first organic mineral containing glycolate, from the Santa Catalina Mountains, Tucson, Arizona, U.S.A.

Abstract A new organic mineral species, lazaraskeite, ideally Cu(C2H3O3)2 with two polytypes M1 and M2, was discovered in the high elevation of the Santa Catalina Mountains, north of Tucson, Arizona, U.S.A. Both lazaraskeite-M1 and -M2 occur as euhedral individual crystals (up to 0.20 × 0.20 × 0.80 mm) or aggregates, with the former being more equant crystals and the latter bladed crystals elongated along the c axis. Associated minerals include chrysocolla, malachite, wulfenite, mimetite, hydroxylpyromorphite, hematite, microcline, muscovite, and quartz. Both polytypes are greenish-blue in transmitted light, transparent with white streak, and a vitreous luster. They are brittle and have a Mohs hardness of ~2; cleavage is perfect on {101}. No parting or twinning was observed. The measured and calculated densities are 2.12(2) and 2.138 g/cm3, respectively, for lazaraskeite-M1 and 2.10(2) and 2.086 g/cm3 for lazaraskeite-M2. Optically, lazaraskeite-M1 is biaxial (−), with α = 1.595(3), β = 1.629(8), γ = 1.645(5), 2Vmeas = 69(2)°, 2Vcal = 67°. Lazaraskeite-M2 is also biaxial (−), with α = 1.520(5), β = 1.578(6), γ = 1.610(5), 2Vmeas = 73(2)°, 2Vcal = 70°. Lazaraskeite is insoluble in water or acetone. An electron microprobe analysis for Cu and an Elemental Combustion System equipped with mass spectrometry for C yielded an empirical formula, based on 6 O apfu, Cu1.01(C1.99H2.99O3)2 for lazaraskeite-M1 and Cu1.01(C1.98H3.00O3)2 for lazaraskeite-M2. The measured δ13C ‰ values are –37.7(1) and –37.8(1) for lazaraskeite-M1 and -M2, respectively. Both lazaraskeite-M1 and -M2 are monoclinic with the same space group P21/n. The unit-cell parameters are a = 5.1049(2), b = 8.6742(4), c = 7.7566(3) Å, β = 106.834(2)°, V = 328.75(2) Å3 for M1 and a = 5.1977(3), b = 7.4338(4), c = 8.8091(4) Å, β = 101.418(2)°, V = 333.64(3) Å3 for M2. Lazaraskeite-M1 is the natural analog of synthetic bis(glycolato)copper(II), Cu(C2H3O3)2. Its crystal structure is characterized by layers made of octahedrally coordinated Cu2+ cations and glycolate (C2H3O3)– anionic groups. These layers, parallel to (101), are linked together by the strong hydrogen bonds (O-H···O = 2.58 Å). The CuO6 octahedron is highly distorted, with four equatorial Cu-O bonds between 1.92 and 1.94 Å and two axial bonds at 2.54 Å. Lazaraskeite-M2 has the same topology as lazaraskeite-M1 and possesses all structural features of the low-temperature phase transformed from lazaraskeite-M1 at 220 K (Yoneyama et al. 2013). The major differences between the two polytypes of lazaraskeite include: (1) M1 has b &amp;gt; c, with β = 106.8°, whereas M2 has b &amp;lt; c, with β = 101.4°; (2) the CuO6 octahedron in M1 is more elongated and distorted than in M2; and (3) there is a relative change in the molecular orientation between the two structures. Lazaraskeite represents the first organic mineral that contains glycolate. Not only does its discovery imply that more glycolate minerals may be found, but also suggests that glycolate minerals may serve as a potential storage for biologically fixed carbon.

The role of hydrothermal fluids in sedimentation in saline alkaline lakes: Evidence from Nasikie Engida, Kenya Rift Valley

AbstractSaline alkaline lakes that precipitate sodium carbonate evaporites are most common in volcanic terrains in semi‐arid environments. Processes that lead to trona precipitation are poorly understood compared to those in sulphate‐dominated and chloride‐dominated lake brines. Nasikie Engida (Little Magadi) in the southern Kenya Rift shows the initial stages of soda evaporite formation. This small shallow (&lt;2 m deep; 7 km long) lake is recharged by alkaline hot springs and seasonal runoff but unlike neighbouring Lake Magadi is perennial. This study aims to understand modern sedimentary and geochemical processes in Nasikie Engida and to assess the importance of geothermal fluids in evaporite formation. Perennial hot‐spring inflow waters along the northern shoreline evaporate and become saturated with respect to nahcolite and trona, which precipitate in the southern part of the lake, up to 6 km from the hot springs. Nahcolite (NaHCO3) forms bladed crystals that nucleate on the lake floor. Trona (Na2CO3·NaHCO3·2H2O) precipitates from more concentrated brines as rafts and as bottom‐nucleated shrubs of acicular crystals that coalesce laterally to form bedded trona. Many processes modify the fluid composition as it evolves. Silica is removed as gels and by early diagenetic reactions and diatoms. Sulphate is depleted by bacterial reduction. Potassium and chloride, of moderate concentration, remain conservative in the brine. Clastic sedimentation is relatively minor because of the predominant hydrothermal inflow. Nahcolite precipitates when and where pCO2 is high, notably near sublacustrine spring discharge. Results from Nasikie Engida show that hot spring discharge has maintained the lake for at least 2 kyr, and that the evaporite formation is strongly influenced by local discharge of carbon dioxide. Brine evolution and evaporite deposition at Nasikie Engida help to explain conditions under which ancient sodium carbonate evaporites formed, including those in other East African rift basins, the Eocene Green River Formation (western USA), and elsewhere.

Windmountainite, □Fe3+2Mg2□2Si8O20(OH)2(H2O)4·4H2O, a new modulated, layered Fe3+-Mg-silicate-hydrate from Wind Mountain, New Mexico: Characterization and origin, with comments on the classification of palygorskite-group minerals

ABSTRACTWindmountainite, ideally □Fe3+2Mg2□2Si8O20(OH)2(H2O)4·4H2O, is a new mineral species and member of the palygorskite group discovered as orange-brown, radiating aggregates that commonly fill vesicles (average 1.5 × 2.5 mm) within a phonolite dike at Wind Mountain, Otero County, New Mexico, USA. The mineral develops as tightly bound bundles (up to 0.02 × 6 mm) of acicular to bladed crystals that are elongate on [001] and flattened on the pinacoid {010}. Associated minerals include albite, aegirine, fluorapophyllite-(K), natrolite, neotocite, and montmorillonite, the last of these being observed to replace primary windmountainite. It has a dull luster, silky in aggregates, is translucent and has an orange-brown streak. It does not fluoresce under short-, medium-, or long-wave ultraviolet radiation. Windmountainite is brittle with a splintery fracture and has two good cleavages (predicted) on {110}, an estimated hardness of 2, a calculated density of 2.51 g/cm3, and a calculated navg of 1.593. A total of n = 30 EMPA (WDS) analyses from six grains yielded an average of (wt.%): Na2O 0.08, MgO 3.47, Al2O3 1.15, SiO2 49.76, Cl 0.07, K2O 0.40, CaO 0.68, TiO2 0.30, MnO 5.64, Fe2O3 20.17, H2O (calc.) 16.59, O=Cl –0.02, total 98.29. The empirical formula [based on Σ(T1, T2, M2, M3) = 12 cations pfu, excluding Ca, K, and Na] is: (□0.78Ca0.12K0.08Na0.02)Σ1.00(Fe3+1.93Al0.04Ti0.02)Σ1.99 (Mg0.81Mn2+0.75Fe3+0.44)Σ2.00□2(Si7.81Al0.17Ti0.01Fe3+0.01)Σ8.00O20[(OH)1.98Cl0.02]Σ2.00[(H2O)3.38(OH)0.62]Σ4.00·4H2O, yielding the simplified formula, □Fe3+2Mg2□2Si8O20(OH)2(H2O)4·4H2O. The predominance of Fe3+ is based on color, results from the crystal-structure refinement, the crystal-chemistry of palygorskite-group minerals, the association with Fe3+-dominant minerals, and considerations regarding the late-stage geochemical evolution of agpaitic rocks. The presence of H2O and OH was determined based on results from the refined crystal structure and Fourier-transform infrared spectroscopy. Windmountainite crystallizes in the space group C2/m with a 13.759(3), b 17.911(4), c 5.274(1) Å, β 106.44(3)°, V 1246.6(1) Å3, and Z = 2. The seven strongest powder X-ray diffraction lines are [d in Å (I), (hkl)]: 10.592 (100) (110), 5.453 (16) (130), 4.484 (19) (040), 4.173 (28) , 3.319 (53) (221, 400), 2.652 (30) , 2.530 (27) . The crystal structure was determined from single-crystal X-ray diffraction data and refined to R = 4.01% and wR2 = 10.70% using data from 902 reflections (Fo &amp;gt; 4σFo). It is based on sheets of inverted double chains of SiO4 tetrahedra that sandwich ribbons of Mφ6 octahedra (φ = O, OH, H2O, Cl), giving rise to large channels (∼6.5 × 9 Å) that are occupied by loosely held H2O groups. A modified classification of the palygorskite group [general crystal-chemical formula M1M22M32M42T14T24O20(OH)2(H2O,OH)4·W] is proposed based on the occupants of the four M sites. Within this scheme, windmountainite is the □-Fe3+-Mg-□ member. The palygorskite group includes six members: palygorskite (monoclinic and orthorhombic polytypes), yofortierite, tuperssuatsiaite, raite, windhoekite, and windmountainite. Windmountainite is considered to have formed from late-stage fluids that were alkaline, oxidized, and rich in both Fe3+ and H2O; high aH2O conditions are reflective of abundant, hydrated feldspathoids (natrolite and analcime) forming as primary rock-forming minerals in the phonolite at Wind Mountain.

Significance of Fracture-Filling Rose-Like Calcite Crystal Clusters in the SE Pyrenees

Fracture-filling rose-like clusters of bladed calcite crystals are found in the northern sector of the Cadí thrust sheet (SE Pyrenees). This unusual calcite crystal morphology has been characterized by using optical and electron microscope, X-ray diffraction, Raman spectroscopy, δ18O, δ13C, 87Sr/86Sr, clumped isotopes, and major and rare earth elements + yttrium (REEs + Y) analysis. Petrographic observations and powder X-ray diffraction measurements indicate that these bladed crystals are mainly made of massive rhombic crystals with the conventional (104) faces, as well as of possibly younger, less abundant, and smaller laminar crystals displaying (108) and/or ( 1 ¯ 08) rhombic faces. Raman analysis of liquid fluid inclusions indicates the presence of aromatic hydrocarbons and occasionally alkanes. Clumped isotopes thermometry reflects that bladed calcite precipitated from meteoric fluids at ~60–65 °C. The 87Sr/86Sr ratios and major elements and REEs content of calcite indicate that these fluids interacted with Eocene marine carbonates. The presence of younger ‘nailhead’ calcite indicates later migration of shallow fresh groundwater. The results reveal that rose-like calcite clusters precipitated, at least in the studied area, due to a CO2 release by boiling of meteoric waters that mixed with benzene and aromatic hydrocarbons. This mixing decreased the boiling temperature at ~60–65 °C. The results also suggest that the high Sr content in calcite, and probably the presence of proteins within hydrocarbons trapped in fluid inclusions, controlled the precipitation of bladed crystals with (104) rhombohedral faces.

Microbial mineralization of botryoidal laminations in the Upper Ediacaran dolostones, Western Yangtze Platform, SW China

Botryoidal dolostones are abundant in the Second Member of the Upper Ediacaran Dengying Formation in the Western Yangtze Platform. Although they have been extensively discussed as important host rocks for giant gas reservoirs, there is no consensus on the microbial impact on mineralization processes in the botryoidal laminations. Typical botryoidal laminations were studied under optical microscopes and scanning electron microscopes (SEMs) to investigate their origin. There are three macroscopic morphological types of botryoidal lamination: stromatoid lamination, cavity-lining lamination, and spherical-encrusting lamination. These three types of lamination are composed of fibrous and bladed crystals growing perpendicular to the botryoidal laminae, which have hitherto been implicitly considered to be from abiogenic chemical precipitation. There are many lines of new evidence that demonstrate microbial activities in the interbedded dark and bright laminae constituting the laminations. In the dark laminae, euhedral dolomite rhombs are observed sticking to linear and tubular filaments, or wrapped in sheets of extracellular polymeric substances (EPS) with dolomite crystal sizes of generally <5 μm. The bright laminae are dominated by coarser dolomites and connected by radial sheaths and trichomes with dolomite crystal sizes of primarily around 10 μm. Different species of bacteria, which are closely related to the macroscopic morphology of the laminations, are present in both the bright and dark laminae. The results are useful in understanding the origin and formation mechanisms of the Neoproterozoic botryoidal dolostones. The new findings may also shed new light on the occurrence and evolution of early life on Earth in the Precambrian Era.

Hydrothermal influence on barite precipitates in the basal Ediacaran Sete Lagoas cap dolostone, São Francisco Craton, central Brazil

Most Precambrian sediment-hosted barites have been interpreted to be diagenetic, hydrothermal exhalation, or methane-seepage in origin. Seafloor barite precipitates and void-filling barite cements in basal Ediacaran cap dolostones have been interpreted as sedimentary and early diagenetic in origin, and they have been used to infer ocean geochemistry in the aftermath of the terminal Cryogenian (or Marinoan) Snowball Earth glaciation. Barite crystals precipitated syndepositionally from seawater or authigenically from marine porewaters can potentially offer insights into Neoproterozoic ocean geochemistry. In this study, we analyzed void-filling barite cements from the basal Ediacaran Sete Lagoas cap dolostone to determine whether the barite records seawater geochemical signatures and whether it experienced post-depositional hydrothermal alteration. Sete Lagoas barite occurs as veins and major void-filling cement in multiple horizons, sometimes interbedded with carbonate fans. Barite crystals, commonly forming rosettes, grew upwards and downwards as radiating bladed crystals, isolated crystals in the matrix, and inclusions within carbonate fan crystals. Sulfur isotope compositions of coexisting barite and carbonate-associated sulfate (CAS) show similar values, suggesting a similar sulfate source, potentially seawater sulfate from a shallow marine environment. Assuming that CAS was sourced from seawater sulfate, we infer that the Sete Lagoas barite was precipitated from marine porewaters with seawater as a source of the sulfate. Carbonaceous material (CM) and fluid inclusions in barite crystals share a similar thermal history with a peak temperature in the range of 206–257 °C. CM was not detected in the host rock, possibly due to pervasive dolomitization, thermodegradation of CM or the fine-grained nature of the host rock. Estimated temperatures and salinity based on fluid inclusions are both higher than seawater, suggesting that hydrothermal activity, perhaps those related to Mississippi-Valley type mineralization in the São Francisco Craton, may have influenced the Sete Lagoas barite. Thus, although the Sete Lagoas barite may have originally precipitated from seawater or marine porewaters in communication with seawater, it may have been subsequently influenced by hydrothermal activity and therefore a more thorough diagenetic assessment must be done before the Sete Lagoas barites can be used to infer seawater geochemistry and environment in the aftermath of Marinoan Snowball Earth.