The Canadian Mineralogist

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ISSN / EISSN : 0008-4476 / 1499-1276
Published by: Mineralogical Association of Canada (10.3749)
Total articles ≅ 2,410
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I. Stephan Zajac,
The Canadian Mineralogist, Volume 60, pp 417-431; https://doi.org/10.3749/canmin.2000112

Abstract:
The Lower Proterozoic, Lake Superior-type Sokoman Iron Formation of the Labrador Trough is one of the world's largest iron formations. It represents a unique, major event in the history of the Trough. Originally a largely irregularly bedded, intraclastic, granular, locally oolitic, conglomeratic iron formation, it is highly variable in its stratigraphy, mineralogy, and textures, which are the consequence of sedimentology, diagenesis, metamorphism, structural deformation, and magmatic overprint. Despite its complexity, the regional characteristics of the iron formation within the 1200 km length of the Labrador Trough indicate three main stratigraphic units, defined by their dominant iron minerals: the lower and upper parts of the formation are characterized by the abundance of iron silicates and carbonates (silicate-carbonate facies), and the middle part is characterized by the dominance of iron oxides (oxide facies). The origin of these lithostratigraphic units of the iron formation is attributed to three main sea-level changes which changed the chemistry (oxidation–reduction potential) and the physical energy (wave and current action) of the sedimentary environment. The vast amount of iron and some of the silica required for deposition of the Sokoman Formation is inferred to be the consequence of intense hydrothermal activity within a major rift created by the eastward extension of the Labrador Trough ca 1.88 Ga. The hydrothermal fluids venting within the rift saturated the deep and likely anoxic sea of the Trough with ferrous iron and some silica which then upwelled onto its oxygenated shallow waters to deposit the iron formation. The end of the processes involved in creating the iron formation ca. 1.82 Ga is attributed to the westward contraction of the Trough induced by the Hudsonian (Trans-Hudson) orogeny, which closed the iron- and silica-generating rift and at the same time ended all magmatic activities and related sedimentation coeval with the deposition of the iron formation.
, Tatsuya Osako, Akira Miyake
The Canadian Mineralogist, Volume 60, pp 405-416; https://doi.org/10.3749/canmin.2100010

Abstract:
X-ray diffraction experiments were carried out with protoenstatite, chemical composition Mg2Si2O6, in order to clarify the conditions under which protoenstatite can be retained at room temperature. Our results show that grain size, cooling rate, and shear stress during sample preparation clearly affect the transition from protoenstatite to clinoenstatite. Smaller protoenstatite grains were more likely to be retained, and the relationship between the retained volume ratio of the protoenstatite and grain size was statistically consistent with martensitic nucleation. The most protoenstatite was retained in the experiment using a cooling rate of 3 °C/min; the retained volume ratio decreased in experiments with both faster and slower cooling rates. The martensitic transformation of protoenstatite to clinoenstatite is promoted by shear stress caused by a fast cooling rate. Shear stress caused by grinding and polishing also promotes the transformation, but ion milling, used to prepare samples for transmission electron microscope observation, leaves the protoenstatite unchanged. Therefore, samples including protoenstatite should be prepared without producing shear stress so that the protoenstatite can be observed.
, Maxwell C. Day, Frank C. Hawthorne, Fernando Cámara
The Canadian Mineralogist, Volume 60, pp 513-531; https://doi.org/10.3749/canmin.2100049

Abstract:
Selivanovaite, ideally NaFe3+Ti4(Si2O7)2O4(H2O)4, is a murmanite-group (seidozerite supergroup) TS-block mineral from the Lovozero massif, Kola Peninsula, Russia. The crystal structure of selivanovaite was refined in space group C ⁠, a 10.524(6), b 13.815(6), c 12.213(14) Å, α 99.74(6), β 107.45(8), γ 90.15(10)°, V 1666.8(26) Å3, R1 = 21.40%. The previously given chemical analysis has been modified to better fit the crystal structure: Nb2O5 8.51, ZrO2 2.94, TiO2 31.96, SiO2 30.62, Al2O3 0.05, Fe2O3 5.08, FeO 3.23, MnO 3.36, CaO 2.14, MgO 0.75, Na2O 2.47, H2O 8.88, sum 99.99 wt.%; H2O was determined from structure-refinement results: H2O = 3.34 pfu, OH = 1.05 pfu. The empirical formula calculated on 22 O apfu is: (Na0.63Ca0.30Mn0.36)Σ1.29(Fe3+0.50Fe2+0.35)Σ0.85(Ti3.14Nb0.50Zr0.19Mg0.15Mn0.01Al0.01)Σ4.00Si3.99O22.00H7.73, Z = 4. The crystal structure of selivanovaite [basic structure type B1(MG)] is an array of TS blocks (Titanium Silicate) connected via hydrogen bonds. The TS block consists of HOH sheets (H = heteropolyhedral, O = octahedral) parallel to (001). In the O sheet, the Ti-dominant MO(1,2) sites, Na-dominant MO(3) site, and □-dominant MO(4) sites give ideally Na□Ti2pfu. In the H sheet, the Ti-dominant MH(1,2) sites, Fe3+-dominant AP(1) site, and vacant AP(2) sites give ideally Fe3+□Ti2pfu. The MH and AP(1) polyhedra and Si2O7 groups constitute the H sheet. The ideal structural formula of selivanovaite of the form AP2MH2MO4(Si2O7)2(XOM,A)4(XPM,A)4 is Fe3+□Ti2Na□Ti2(Si2O7)2O4(H2O)4. Selivanovaite is a Fe3+-bearing and OH-poor analogue of vigrishinite, ideally Zn□Ti2Na□Ti2(Si2O7)2O2O(OH)(H2O)4. Vigrishinite and selivanovaite are related by the following substitution: O(OH)vig + H(Zn2+)vigO(O2–)sel + H(Fe3+)sel. Selivanovaite is a Fe3+-bearing and Na-poor analogue of murmanite, ideally Na2Ti2Na2Ti2(Si2O7)2O4(H2O)4. Murmanite and selivanovaite are related by the following substitution: O(Na+)mur + H(Na+2)murO(□)sel + H(Fe3+)sel + H(□)sel. The doubling of the t1 and t2 translations of selivanovaite compared to those of murmanite is due to the ordering of Fe3+ and □ in the H sheet and Na and □ in the O sheet of selivanovaite.
, Dirk Schumann
The Canadian Mineralogist, Volume 60, pp 385-403; https://doi.org/10.3749/canmin.2000125

Abstract:
The ore at the Dwyer fluorite mine, near Wilberforce, Ontario, consists of calcite–fluorite dikes that show clear signs of flowage. Those dikes and the large-scale development of fenites at the expense of a granite–monzonite pluton can only be explained by the existence of a subjacent body of carbonatite. The dikes consist of ribbons of calcite and fluorite and contain subhedral crystals of fluorapatite aligned with the ribbons. The dikes also carry crystals of aegirine-augite, titanite, and bastnäsite-(Ce). Both the fluorapatite and aegirine-augite contain micrometric globules of boundary-layer melt that crystallized in situ to calcite, fluorite, quartz, bastnäsite-(Ce), hematite, and titanite. Fragments of the REE-enriched fenite show signs of incipient rheomorphism at a temperature estimated to be at least 725 °C. The large-scale alkali metasomatism occurred toward the end of the Grenville orogenic cycle, at a time of crustal relaxation, roughly 200 million years after emplacement of a granite–monzonite pluton. By analogy with occurrences elsewhere, it is likely that the carbonatitic melt separated immiscibly from a nepheline syenitic parental melt. Fluor-calciocarbonatitic magmatism likely is genetically linked to the U and Th mineralization in the area and contributed to the unusual geological complexity of the Bancroft–Haliburton region.
Sourav Bhattacharjee, Monojit Dey, , Roger H. Mitchell, Minghua Ren
The Canadian Mineralogist, Volume 60, pp 469-484; https://doi.org/10.3749/canmin.2100058

Abstract:
The existing classification of pyrochlore group minerals is essentially based on the dominant valence rule. However, coupled heterovalent-homovalent substitutions at the A-, B-, and Y-sites commonly result in charge-imbalanced endmember formulae. The application of the site total charge (STC) method permits the determination of a charge-balanced endmember. Species names are assigned by using the dominant constituent rule. According to the current IMA nomenclature scheme, some previously established pyrochlore species, such as kalipyrochlore, strontiopyrochlore, bariopyrochlore, plumbopyrochlore, ceriopyrochlore, yttropyrochlore, bismutopyrochlore, and uranpyrochlore, are all grouped as zero-valent-dominant pyrochlores, resulting in the loss of petrogenetic information. In this work, the zero-valent-dominant pyrochlores of the pyrochlore group (sensu stricto) are classified into R+-, R2+-, R3+-, and R4+-pyrochlores where the respective cations (R) are the dominant valencies at the A- and Y-sites (for R+-pyrochlores) after vacancies (□) and H2O. The endmember charge arrangements are determined by the STC method to obtain charge-balanced endmember formulae for all possible zero-valent pyrochlore species. It is recommended that suitable adjectival modifiers be used along with the species name to emphasize the abundance of certain cations, which may or may not be reflected in the endmember formula. This approach would facilitate the usage of pyrochlore group minerals for all practical petrological and exploration purposes. It is considered that pyrochlores with significant A-site vacancies do not necessarily reflect formation in a supergene environment, as such pyrochlores can also form in hydrothermal parageneses.
, John M. Hughes, Barbara P. Nash, Jason B. Smith
The Canadian Mineralogist, Volume 60, pp 543-554; https://doi.org/10.3749/canmin.210015

Abstract:
Donowensite (IMA2020-067), Ca(H2O)3Fe3+2(V2O7)2, and mikehowardite (IMA2020-068), Fe3+4(VO4)4(H2O)2·H2O, are intimately associated new secondary minerals from the Wilson Springs vanadium mine, Wilson Springs, Arkansas, USA. Donowensite has the following properties: needles up to 1 mm in length; yellow color; orange streak; subadamantine luster; brittle; Mohs hardness 3; splintery fracture; three cleavages ({001} perfect, {100} and {010} very good); density 2.97(2) g/cm3; biaxial (+), α > 1.95, β > 1.95, γ > 1.95; 2V = 72(2)°; moderate r > v dispersion; orientation X ^ b = 7°, Zc; pleochroism X brown orange, Y orange yellow, Z yellow. Mikehowardite has the following properties: equant prisms up to 0.15 mm in length; very dark brown color; yellow-orange streak; subadamantine luster; Mohs hardness 3½; irregular, stepped fracture; three cleavages ({100} very good, two undetermined good cleavages); density 3.19(2) g/cm3; biaxial with slight pleochroism in shades of brown-orange; Gladstone-Dale nav = 2.034. Electron probe microanalyses provided the empirical formulae Ca0.93Fe3+1.92Mn3+0.01V4.06P0.01O17H6.00 for donowensite and K0.11Ca0.02Fe3+3.78Mn3+0.03V3.67P0.33O18.87H6.18 for mikehowardite. Donowensite is triclinic, P with a = 7.3452(4), b = 9.9291(4), c = 10.0151(7) Å, α = 94.455(7), β = 98.476(7), γ = 100.779(7)°, V = 705.52(7) Å3, and Z = 2. Mikehowardite is triclinic, P with a = 6.6546(17), b = 6.6689(14), c = 9.003(2) Å, α = 76.515(5), β = 84.400(6), γ = 75.058(5)°, V = 375.11(15) Å3, and Z = 1. The structure of donowensite (R1 = 0.0561 for 2615 I > 2σI reflections) contains zig-zag chains of edge-sharing FeO6 octahedra that are linked to one another by V2O7 pyrovanadate groups to form sheets between which are Ca2+ cations and H2O groups. The structure of mikehowardite (R1 = 0.0678 for 1098 I > 2σI reflections) has similarities to the structure of schubnelite. In both mikehowardite and schubnelite, edge-sharing dimers of Fe3+O6 octahedra are linked by distorted VO4 tetrahedra.
Yiguan Lu, C. Michael Lesher, Liqiang Yang, Matthew I. Leybourne, Wenyan He, Mingwei Yuan, Zhen Yang, Xue Gao
The Canadian Mineralogist, Volume 60, pp 555-557; https://doi.org/10.3749/canmin.er00003

, Maxwell C. Day, Frank C. Hawthorne, Fernando Cámara
The Canadian Mineralogist, Volume 60, pp 493-512; https://doi.org/10.3749/canmin.2100016

Abstract:
Shkatulkalite, ideally Na5TiNb2(Si2O7)2O3F(H2O)7, is a lamprophyllite-group (seidozerite supergroup) TS-block mineral from the Lovozero massif, Kola Peninsula, Russia. The crystal structure of shkatulkalite was refined as triclinic, space group P ⁠, a 5.464(1), b 7.161(1), c 15.573(1) Å, α 90.00(3), β 95.75(3), γ 90.00(3)°, V 606.3(4) Å3, R1 = 7.26%. The previously given chemical analysis has been modified to better fit the crystal structure: Nb2O5 24.15, TiO2 11.35, SiO2 27.22, BaO 1.15, SrO 2.20, MnO 1.68, CaO 0.46, K2O 0.29, Na2O 14.78, H2O 15.27, F 1.61, O = F −0.68, sum 99.48 wt.%; H2O was determined from structure-refinement results. The empirical formula was calculated on 25.27 (O + F) apfu (in accord with the crystal structure): (Na1.40Sr0.19Ba0.07K0.05)Σ1.71(Na2.86Mn0.10Ca0.07)Σ3.03(Nb1.62Ti1.27Mn0.11)Σ3Si4.03O24.52H15.11F0.75, Z = 1. The ideal structural formula is as follows: Na2Nb2Na3Ti(Si2O7)2O2(FO)(H2O)4(H2O)3. The crystal structure of shkatulkalite [basic structure type B5(LG)] is a combination of a TS (titanium-silicate) block and an I (intermediate) block. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral). The TS block exhibits linkage and stereochemistry typical for the lamprophyllite group where Ti (+ Nb + Fe3+ + Mg) = 3 apfu. The O sheet is composed of Ti-dominant MO(1) and Na-dominant MO(2,3) octahedra. In the H sheet in shkatulkalite, Si2O7 groups link to Nb-dominant MH octahedra. The AP site occurs in the plane of the H sheet and splits into AP(1) and AP(2) sites, occupied by Na at 70% and Sr (less Ba and K) at 11%. The I block consists of H2O groups. The I block of shkatulkalite is topologically identical to those in the derivative structures of kazanskyite and nechelyustovite. The structure of the lamprophyllite-group mineral shkatulkalite has a counterpart structure in the murmanite group (Ti = 4 apfu): kolskyite, ideally Na2CaTi4(Si2O7)2O4(H2O)7 [basic structure type B7(MG)]: the two structures have TS blocks of different topology and similar I blocks, mainly occupied by H2O groups.
, Xiangping Gu, Thomas Loomis, Ronald B. Gibbs, Robert T. Downs
The Canadian Mineralogist, Volume 60, pp 485-492; https://doi.org/10.3749/canmin.2100029

Abstract:
An occurrence of malhmoodite, Fe2+Zr(PO4)2·4H2O, from the Scott's Rose Quartz mine, Custer County, South Dakota, USA, has been identified. It occurs as divergent groups of yellowish, flat-lying platy crystals on football-size masses of altered löllingite with scorodite, parasymplesite, karibibite, schneiderhöhnite, kahlerite, and zircon. An electron probe microanalysis of malhmoodite yielded an empirical formula (based on 12 O apfu) of Fe1.06(Zr1.10Hf0.03)Σ1.13[(P0.93As0.01)Σ0.94O4]2·4H2O. Single-crystal X-ray structure analysis shows that malhmoodite is the Fe-analogue of zigrasite, MgZr(PO4)2·4H2O. Malhmoodite is triclinic with space group P and unit-cell parameters a = 5.31200(10), b = 9.3419(3), c = 9.7062(3) Å, α = 97.6111(13), β = 91.9796(11), γ = 90.3628(12)°, V = 477.10(2) Å3, Z = 2, in contrast to the previously reported monoclinic symmetry with space group P21/c and unit-cell parameters a = 9.12(2), b = 5.42(1), c = 19.17(2) Å, β = 94.8(1)°, V = 944.26 Å3, Z = 4. The crystal structure of malhmoodite is characterized by sheets composed of ZrO6 octahedra sharing all vertices with PO4 tetrahedra. These sheets are parallel to (001) and are joined together by the FeO2(H2O)4 octahedra. The structure determination of malhmoodite, along with that of zigrasite, warrants a re-investigation of synthetic compounds M2+Zr(PO4)2·4H2O (M = Mn, Ni, Co, Cu, or Zn) that have been assumed previously to be monoclinic.
Ting Li, Guang Fan, Xiangkun Ge, Tao Wang, Apeng Yu, Liumin Deng
The Canadian Mineralogist, Volume 60, pp 533-542; https://doi.org/10.3749/canmin.2000127

Abstract:
Tengchongite, a uranyl molybdate mineral from Tengchong County, Yunnan Province, China, was originally described as orthorhombic, with space group A2122, unit-cell parameters a = 15.616(4) Å, b = 13.043(6) Å, c = 17.716(14) Å, V = 3608 Å3, and an ideal chemistry CaO·6UO2·2MO3·12H2O. Its ideal chemical formula is given as Ca(UO2)6(MoO4)2O5·12H2O in the current IMA-CNMNC List of Mineral Names. Tengchongite is the only mineral with a U:Mo ratio of 3:1, the second-highest ratio of all natural and synthetic uranyl molybdate materials, but its crystal structure remained undetermined until now. This study reports the structure determination of tengchongite from the type sample and a revision of its chemical formula to Ca(UO2)6(MoO4OH)2O2(OH)4·9H2O. Tengchongite is orthorhombic, with space group C2221, Z = 4, a = 13.0866(8) Å, b = 17.6794(12) Å, c = 15.6800(9) Å, and V = 3627.8(4) Å3. Its crystal structure was refined from single-crystal X-ray diffraction data to R1 = 0.0323 for 6055 unique observed reflections. The fundamental building blocks of the tengchongite structure are sheets consisting of six-membered clusters of edge-sharing UO7 pentagonal bipyramids, which are connected by sharing vertices among them, as well as edges and vertices with MoO5 trigonal bipyramids. These sheets, parallel to [010], are linked together by Ca2+ and H2O groups. Tengchongite represents a new type of structural connectivity between U- and Mo-polyhedra for uranyl molybdate minerals.
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