Topical Collection "New Minerals"

Editors

Prof. Dr. Irina O. Galuskina
Website
Collection Editor
Department of Geochemistry, University of Silesia in Katowice, Katowice, Poland
Interests: new minerals; crystal chemistry; pyrometamorphic rocks; skarns; rodingites; Raman spectroscopy; crystal growth
Special Issues and Collections in MDPI journals
Prof. Dr. Igor V. Pekov
Website
Collection Editor
Department of Mineralogy, Lomonosov Moscow State University, Moscow 119991, Russia
Interests: mineralogy; crystal chemistry of minerals and inorganic compounds; rare elements; microporous materials; geochemistry of alkaline rocks and postvolcanic processes
Special Issues and Collections in MDPI journals
Prof. Dr. Luca Bindi
Website
Collection Editor
Dipartimento di Scienze della Terra, Università di Firenze, 50121, Florence, Italy
Interests: aperiodic crystals; coordination chemistry; crystal chemistry; phase transitions; sulfides; sulfosalts; structural chemistry; determination of structure; twinning; X-ray diffraction

Topical Collection Information

Dear Colleagues,

The number of new minerals has increased continuously in recent years, reaching almost 200 new species in 2018. This great bunch of discoveries calls for a proper place to publish their descriptions and characterizations. We strongly believe that this topical collection of the journal Minerals could be the right place to report such accounts.

New minerals are becoming more and more important for the improvement of the knowledge about processes relevant for Earth and planets with possible know-how transfer to environmental and material sciences. They are indeed messengers about the way Earth works, from the mantle to the surficial environments. In the present society, a deep knowledge of (new) minerals are becoming increasingly important, not only because they are the source of several useful metals, but also for their interesting applications in high-tech fields. Therefore, by increasing the knowledge of new minerals we could increase the understanding of the past, present, and future of our planet.

Prof. Dr. Irina O. Galuskina
Prof. Dr. Igor V. Pekov
Prof. Dr. Luca Bindi
Collection Editors

Manuscript Submission Information

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Keywords

  • new minerals
  • crystal structure
  • crystal chemistry
  • new structure type
  • mineral group
  • mineral supergroup
  • mineral classification

Related Special Issue

Published Papers (9 papers)

2020

Jump to: 2019

Open AccessArticle
Chromium Members of the Pumpellyite Group: Shuiskite-(Cr), Ca2CrCr2[SiO4][Si2O6(OH)](OH)2O, a New Mineral, and Shuiskite-(Mg), a New Species Name for Shuiskite
Minerals 2020, 10(5), 390; https://doi.org/10.3390/min10050390 - 26 Apr 2020
Abstract
A new pumpellyite-group mineral shuiskite-(Cr), ideally Ca2CrCr2[SiO4][Si2O6(OH)](OH)2O, was found at the Rudnaya mine, Glavnoe Saranovskoe deposit, Middle Urals, Russia. It occurs on the walls of 0.5 to 1 cm thick fractures [...] Read more.
A new pumpellyite-group mineral shuiskite-(Cr), ideally Ca2CrCr2[SiO4][Si2O6(OH)](OH)2O, was found at the Rudnaya mine, Glavnoe Saranovskoe deposit, Middle Urals, Russia. It occurs on the walls of 0.5 to 1 cm thick fractures in chromitite, filled with calcite, Cr-bearing clinochlore, and uvarovite. Shuiskite-(Cr) forms long prismatic to acicular crystals up to 0.1 × 0.5 × 7 mm elongated along [010] and slightly flattened on [100]. The crystals are commonly combined into radial, sheaf-like aggregates. Most observed crystals are simple twins with a (001) composition plane. Shuiskite-(Cr) is greenish-black under daylight or purplish-black under incandescent light. It is optically biaxial (–), α = 1.757(5), β = 1.788(6), γ = 1.794(6), 2V (meas.) = 45(10)°, 2V (calc.) = 46° (589 nm). The Dcalc is 3.432 g/cm3. The IR spectrum is reported. The chemical composition (wt.%) is CaO 21.33, MgO 3.17, Al2O3 5.41, Cr2O3 28.50, TiO2 0.18, SiO2 33.86, H2O 5.82, total 98.27. The empirical formula calculated based on the sum of eight metal cations and Si atoms per formula unit is Ca2.02Mg0.42Cr3+1.99Al0.56Ti0.01Si3.00O10.57(OH)3.43. The simplified formula is Ca2(Cr,Mg)(Cr,Al)2[SiO4][Si2O6(OH,O)](OH,O)(OH)2. Shuiskite-(Cr) is monoclinic, C2/m, a = 19.2436(6), b = 5.9999(2), c = 8.8316(3) Å, β = 97.833(3)°, V = 1010.17(6) Å3, and Z = 4. The crystal structure, solved from single-crystal X-ray diffraction data (R = 0.0469), is based on a pair of chains of edge-sharing Cr-centred octahedra running along the b axis, linked together via the [SiO4] and [Si2O6(OH)] groups and Ca-centred polyhedra. The mineral species shuiskite, ideally Ca2MgCr2[SiO4][Si2O6(OH)](OH)3, was renamed to shuiskite-(Mg) by the decision of the IMA CNMNC. The shuiskite solid solution series with the general formula Ca2XCr2[SiO4][Si2O6(OH,O)](OH)2(OH,O), which includes shuiskite-(Mg) and shuiskite-(Cr) with X = Mg and Cr3+, respectively, appeared in the pumpellyite group. Full article
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Open AccessArticle
Kesebolite-(Ce), CeCa2Mn(AsO4)[SiO3]3, a New REE-Bearing Arsenosilicate Mineral from the Kesebol Mine, Åmål, Västra Götaland, Sweden
Minerals 2020, 10(4), 385; https://doi.org/10.3390/min10040385 - 24 Apr 2020
Abstract
Kesebolite-(Ce), ideal formula CeCa2Mn(AsO4)[SiO3]3, is a new mineral (IMA No. 2019-097) recovered from mine dumps at the Kesebol Mn-(Fe-Cu) deposit in Västra Götaland, Sweden. It occurs with rhodonite, baryte, quartz, calcite, talc, andradite, rhodochrosite, K-feldspar, [...] Read more.
Kesebolite-(Ce), ideal formula CeCa2Mn(AsO4)[SiO3]3, is a new mineral (IMA No. 2019-097) recovered from mine dumps at the Kesebol Mn-(Fe-Cu) deposit in Västra Götaland, Sweden. It occurs with rhodonite, baryte, quartz, calcite, talc, andradite, rhodochrosite, K-feldspar, hematite, gasparite-(Ce), chernovite-(Y) and ferriakasakaite-(Ce). It forms mostly euhedral crystals, with lengthwise striation. The mineral is dark grayish-brown to brown, translucent, with light brown streak. It is optically biaxial (+), with weak pleochroism, and ncalc = 1.74. H = 5–6 and VHN100 = 825. Fair cleavage is observed on {100}. The calculated density is 3.998(5) g·cm−3. Kesebolite-(Ce) is monoclinic, P21/c, with unit-cell parameters from X-ray single-crystal diffraction data: a = 6.7382(3), b = 13.0368(6), c = 12.0958(6) Å, β = 98.578(2)°, and V = 1050.66(9) Å3, with Z = 4. Strongest Bragg peaks in the X-ray powder pattern are: [I(%), d(Å) (hkl)] 100, 3.114 (20-2); 92, 2.924 (140); 84, 3.138 (041); 72, 2.908 (014); 57, 3.228 (210); 48, 2.856 (042); 48, 3.002 (132). The unique crystal structure was solved and refined to R1 = 4.6%. It consists of 6-periodic single silicate chains along (001); these are interconnected to infinite (010) strings of alternating, corner-sharing MnO6 and AsO4 polyhedra, altogether forming a trellis-like framework parallel to (100). Full article
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Open AccessArticle
Fluorluanshiweiite, KLiAl1.50.5(Si3.5Al0.5)O10F2, a New Mineral of the Mica Group from the Nanyangshan LCT Pegmatite Deposit, North Qinling Orogen, China
Minerals 2020, 10(2), 93; https://doi.org/10.3390/min10020093 - 21 Jan 2020
Abstract
A new mineral species of the mica group, fluorluanshiweiite, ideally KLiAl1.50.5(Si3.5Al0.5)O10F2, has been found in the Nanyangshan LCT (Li, Cs, Ta) pegmatite deposit in North Qinling Orogen (NQO), central China. Fluorluanshiweiite [...] Read more.
A new mineral species of the mica group, fluorluanshiweiite, ideally KLiAl1.50.5(Si3.5Al0.5)O10F2, has been found in the Nanyangshan LCT (Li, Cs, Ta) pegmatite deposit in North Qinling Orogen (NQO), central China. Fluorluanshiweiite can be regarded as the F-dominant analogue at the A site of luanshiweiite or the K-dominant analogue at the I site of voloshinite. It appears mostly in cookeite as a flaky residue, replaced by Cs-rich mica, or in the form of scale aggregates. Most individual grains are <1 mm in size, with the largest being ca. 1 cm, and the periphery is replaced by cookeite. No twinning is observed. The mineral is silvery white as a hand specimen, and in a thin section, it appears grayish-white to colorless, transparent with white streaks, with vitreous luster and pearliness on cleavage faces. It is flexible with micaceous fracture; the Mohs hardness is approximately 3; the cleavage is perfect on {001}; and no parting is observed. The measured and calculated densities are 2.94(3) and 2.898 g/cm3, respectively. Optically, fluorluanshiweiite is biaxial (–), with α = 1.554(1), β = 1.581(1), γ = 1.583(1) (white light), 2V(meas.) = 25° to 35°, 2V(calc.) = 30.05°. The calculated compatibility index based on the empirical formula is −0.014 (superior). An electron microprobe analysis yields the empirical formula calculated based on 10 O atoms and 2 additional anions of (K0.85Rb0.12Cs0.02Na0.03)Σ1.02[Li1.05Al1.44(□0.47Fe0.01Mn0.02)Σ0.5] Σ2.99(Si3.55Al0.45) Σ4O10F2, which can be simplified to KLiAl1.50.5(Si3.5Al0.5)O10F2. Fluorluanshiweiite is monoclinic with the space group C2/m and unit cell parameters a = 5.2030(5), b = 8.9894(6), c = 10.1253(9) Å, β = 100.68(1)°, and V = 465.37(7) Å3. The strongest eight lines in the X-ray diffraction data are [d in Å(I)(hkl)]: 8.427(25) (001), 4.519(57) (020), 4.121(25) (021), 3.628(61) (112), 3.350(60) (022), 3.091(46) (112), 2.586(100) (130), and 1.506(45) (312). Full article
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2019

Jump to: 2020

Open AccessArticle
Crystal-Chemistry of Sulfates from the Apuan Alps (Tuscany, Italy). VII. Magnanelliite, K3Fe3+2(SO4)4 (OH)(H2O)2, a New Sulfate from the Monte Arsiccio Mine
Minerals 2019, 9(12), 779; https://doi.org/10.3390/min9120779 - 12 Dec 2019
Cited by 1
Abstract
The new mineral species magnanelliite, K3Fe3+2(SO4)4(OH)(H2O)2, was discovered in the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy. It occurs as steeply terminated prisms, up to 0.5 mm in length, yellow [...] Read more.
The new mineral species magnanelliite, K3Fe3+2(SO4)4(OH)(H2O)2, was discovered in the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy. It occurs as steeply terminated prisms, up to 0.5 mm in length, yellow to orange-yellow in color, with a vitreous luster. Streak is pale yellow, Mohs hardness is ca. 3, and cleavage is good on {010}, fair on {100}. The measured density is 2.82(3) g/cm3. Magnanelliite is optically biaxial (+), with α = 1.628(2), β = 1.637(2), γ = 1.665(2) (white light), 2Vmeas = 60(2)°, and 2Vcalc = 59.9°. It exhibits a strong dispersion, r > v. The optical orientation is Y = b, X ^ c ~ 25° in the obtuse angle β. It is pleochroic, with X = orange yellow, Y and Z = yellow. Magnanelliite is associated with alum-(K), giacovazzoite, gypsum, jarosite, krausite, melanterite, and scordariite. Electron microprobe analyses give (wt.%): SO3 47.82, TiO2 0.05, Al2O3 0.40, Fe2O3 25.21, MgO 0.07, Na2O 0.20, K2O 21.35, H2Ocalc 6.85, total 101.95. On the basis of 19 anions per formula unit, assuming the occurrence of one (OH) and two H2O groups, the empirical chemical formula of magnanelliite is (K2.98Na0.04)Σ3.02(Fe3+2.08Al0.05Mg0.01)Σ2.14S3.93O16(OH)(H2O)2. The ideal end-member formula can be written as K3Fe3+2(SO4)4(OH)(H2O)2. Magnanelliite is monoclinic, space group C2/c, with a = 7.5491(3), b = 16.8652(6), c = 12.1574(4) Å, β = 94.064(1)°, V = 1543.95(10) Å3, Z = 4. Strongest diffraction lines of the observed X-ray powder pattern are [d(in Å), estimated visual intensity, hkl]: 6.9, medium, 021 and 110; 4.91, medium-weak, 022; 3.612, medium-weak, 1 ¯ 32, 023, and 1 ¯ 13; 3.085, strong, 202, 150, and 1 ¯ 33; 3.006, medium, 004, 1 ¯ 51, and 151; 2.704, medium, 152 and 2 ¯ 23; 2.597, medium-weak, 2 ¯ 42; 2.410, medium-weak, 153. The crystal structure of magnanelliite has been refined using X-ray single-crystal data to a final R1 = 0.025, on the basis of 2411 reflections with Fo > 4σ(Fo) and 144 refined parameters. The crystal structure is isotypic with that of alcaparrosaite, K3Ti4+Fe3+(SO)4O(H2O)2. Full article
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Open AccessFeature PaperArticle
A New Mineral Ferrisanidine, K[Fe3+Si3O8], the First Natural Feldspar with Species-Defining Iron
Minerals 2019, 9(12), 770; https://doi.org/10.3390/min9120770 - 11 Dec 2019
Cited by 1
Abstract
Ferrisanidine, K[Fe3+Si3O8], the first natural feldspar with species-defining iron, is an analogue of sanidine bearing Fe3+ instead of Al. It was found in exhalations of the active Arsenatnaya fumarole at the Second scoria cone of the [...] Read more.
Ferrisanidine, K[Fe3+Si3O8], the first natural feldspar with species-defining iron, is an analogue of sanidine bearing Fe3+ instead of Al. It was found in exhalations of the active Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Fissure Tolbachik Eruption, Tolbachik volcano, Kamchatka Peninsula, Russia. The associated minerals are aegirine, cassiterite, hematite, sylvite, halite, johillerite, arsmirandite, axelite, aphthitalite. Ferrisanidine forms porous crusts composed by cavernous short prismatic crystals or irregular grains up to 10 μm × 20 μm. Ferrisanidine is transparent, colorless to white, the lustre is vitreous. Dcalc is 2.722 g·cm−3. The chemical composition of ferrisanidine (wt. %, electron microprobe) is: Na2O 0.25, K2O 15.15, Al2O3 0.27, Fe2O3 24.92, SiO2 60.50, in total 101.09. The empirical formula calculated based on 8 O apfu is (K0.97Na0.03)Ʃ1.00(Si3.03Fe3+0.94Al0.02)Ʃ3.99O8. The crystal structure of ferrisanidine was studied using the Rietveld method, the final R indices are: Rp = 0.0053, Rwp = 0.0075, R1 = 0.0536. Parameters of the monoclinic unit cell are: a = 8.678(4), b = 13.144(8), c = 7.337(5) Å, β = 116.39(8)°, V = 749.6(9) Å3. Space group is C2/m. The crystal structure of ferrisanidine is based on the sanidine-type “ferrisilicate” framework formed by disordered [SiO4] and [Fe3+O4] tetrahedra. Full article
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Open AccessArticle
Crystal Chemistry of Sulfates from the Apuan Alps (Tuscany, Italy). V. Scordariite, K8(Fe3+0.670.33)[Fe3+3O(SO4)6(H2O)3]2(H2O)11: A New Metavoltine-Related Mineral
Minerals 2019, 9(11), 702; https://doi.org/10.3390/min9110702 - 13 Nov 2019
Cited by 3
Abstract
The new mineral species scordariite, K8(Fe3+0.670.33)[Fe3+3O(SO4)6(H2O)3]2(H2O)11, was discovered in the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy. It occurs [...] Read more.
The new mineral species scordariite, K8(Fe3+0.670.33)[Fe3+3O(SO4)6(H2O)3]2(H2O)11, was discovered in the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy. It occurs as pseudo-hexagonal tabular crystals, yellowish to brownish in color, up to 0.5 mm in size. Cleavage is perfect on {0001}. It is associated with giacovazzoite, krausite, gypsum, jarosite, alum-(K), and magnanelliite. Electron microprobe analyses give (wt %): SO3 47.31, Al2O3 0.66, Fe2O3 24.68, FeO 0.69, Na2O 0.52, K2O 17.36, H2Ocalc 15.06, total 106.28. The partitioning of Fe between Fe2+ and Fe3+ was based on Mössbauer spectroscopy. On the basis of 67 O atoms per formula unit, the empirical chemical formula is (K7.50Na0.34)Σ7.84(Fe3+6.29Al0.26Fe2+0.20)Σ6.75S12.02O50·17H2O. The ideal end-member formula can be written as K8(Fe3+0.670.33)[Fe3+3O(SO4)6(H2O)3]2(H2O)11. Scordariite is trigonal, space group R-3, with (hexagonal setting) a = 9.7583(12), c = 53.687(7) Å, V = 4427.4(12) Å3, Z = 3. The main diffraction lines of the observed X-ray powder pattern are [d(in Å), estimated visual intensity]: 8.3, strong; 6.6, medium; 3.777, medium; 3.299, medium; 3.189, medium; 2.884, strong. The crystal structure of scordariite has been refined using X-ray single-crystal data to a final R1 = 0.057 on the basis of 1980 reflections with Fo > 4σ(Fo) and 165 refined parameters. It can be described as a layered structure formed by three kinds of layers. As with other metavoltine-related minerals, scordariite is characterized by the occurrence of the [Fe3+3O(SO4)6(H2O)3]5− heteropolyhedral cluster. Full article
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Open AccessArticle
Manganiakasakaite-(La) and Ferriakasakaite-(Ce), Two New Epidote Supergroup Minerals from Piedmont, Italy
Minerals 2019, 9(6), 353; https://doi.org/10.3390/min9060353 - 09 Jun 2019
Abstract
Two new monoclinic (P21/m) epidote supergroup minerals manganiakasakaite-(La) and ferriakasakaite-(Ce) were found in the small Mn ore deposit of Monte Maniglia, Bellino, Varaita Valley, Cuneo Province, Piedmont, Italy. Manganiakasakaite-(La) occurs as subhedral grains embedded in pyroxmangite. Its [...] Read more.
Two new monoclinic (P21/m) epidote supergroup minerals manganiakasakaite-(La) and ferriakasakaite-(Ce) were found in the small Mn ore deposit of Monte Maniglia, Bellino, Varaita Valley, Cuneo Province, Piedmont, Italy. Manganiakasakaite-(La) occurs as subhedral grains embedded in pyroxmangite. Its empirical formula is A(1)(Ca0.62Mn2+0.38) A(2)(La0.52Nd0.08Pr0.07Ce0.07Y0.01Ca0.25) M(1)(Mn3+0.52Fe3+0.28Al0.18V3+0.01) M(2)Al1.00 M(3)(Mn2+0.60Mn3+0.27Mg0.13) T(1−3)(Si2.99Al0.01) O12 (OH), corresponding to the end-member formula CaLaMn3+AlMn2+(Si2O7)(SiO4)O(OH). Unit-cell parameters are a = 8.9057(10), b = 5.7294(6), c = 10.1134(11) Å, β = 113.713(5)°, V = 472.46(9) Å3, Z = 2. The crystal structure of manganiakasakaite-(La) was refined to a final R1 = 0.0262 for 2119 reflections with Fo > 4σ(Fo) and 125 refined parameters. Ferriakasakaite-(Ce) occurs as small homogeneous domains within strongly inhomogeneous prismatic crystals, where other epidote supergroup minerals coexist [manganiandrosite-(Ce), “androsite-(Ce)”, and epidote]. Associated minerals are calcite and hematite. Its empirical formula is A(1)(Ca0.64Mn2+0.36) A(2)(Ce0.37La0.17Nd0.06Pr0.03Ca0.350.02) M(1)(Fe3+0.61Al0.39) M(2)Al1.00 M(3)(Mn2+0.64Mn3+0.33Fe3+0.02Mg0.01) T(1−3)Si3.01 O12 (OH), the end-member formula being CaCeFe3+AlMn2+(Si2O7)(SiO4)O(OH). Unit-cell parameters are a = 8.9033(3), b = 5.7066(2), c = 10.1363(3) Å, β = 114.222(2)°, V = 469.66(3) Å3, Z = 2. The crystal structure of ferriakasakaite-(Ce) was refined to a final R1 = 0.0196 for 1960 unique reflections with Fo > 4σ(Fo) and 124 refined parameters. Full article
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Open AccessFeature PaperArticle
Tsikourasite, Mo3Ni2P1+x (x < 0.25), a New Phosphide from the Chromitite of the Othrys Ophiolite, Greece
Minerals 2019, 9(4), 248; https://doi.org/10.3390/min9040248 - 24 Apr 2019
Cited by 4
Abstract
Tsikourasite, Mo3Ni2P1+x (x < 0.25), is a new phosphide discovered in a mantle-hosted podiform chromitite collected in the abandoned mine of Agios Stefanos (Othrys ophiolite), Central Greece. It forms tiny grains (from a few μm up [...] Read more.
Tsikourasite, Mo3Ni2P1+x (x < 0.25), is a new phosphide discovered in a mantle-hosted podiform chromitite collected in the abandoned mine of Agios Stefanos (Othrys ophiolite), Central Greece. It forms tiny grains (from a few μm up to about 80 μm) and occurs as isolated grains or associated with other known minerals such as nickelphosphide and awaruite, and with undetermined minerals such as Ni-allabogdanite or Ni-barringerite and a V-sulphide. Tsikourasite is brittle and has a metallic luster. In plane-polarized light, tsikourasite is white yellow and it shows no bireflectance, anisotropism or pleochroism. Internal reflections were not observed, Reflectance values of tsikourasite in air (R in %) are: 55.7 at 470 nm, 56.8 at 546 nm, 57.5 at 589 nm and 58.5 at 650 nm. Five spot analyses of tsikourasite give the average composition: P 7.97, S 0.67, V 14.13, Fe 14.37, Co 7.59, Ni 23.9, and Mo 44.16, total 99.60 wt.%, corresponding to the empirical formula (Mo1.778V1.071Fe0.082Co0.069)Σ3.000(Ni1.572Co0.428)Σ2.000(P0.981S0.079)Σ1.060, on the basis of Σ(Mo +V + Fe + Co + Ni) = 5 apfu and taking into account the structural results. The simplified formula is Mo3Ni2P1+x (x < 0.25). The density, which was calculated based on the empirical formula and single-crystal data, is 9.182 g/cm3. The mineral is cubic, space group F-43m, with a = 10.8215(5) Å and Z = 16. Although tsikourasite is similar in composition to those of monipite (MoNiP), polekhovskyite (MoNiP2), and the synthetic compound MoNiP2, all these phases are hexagonal and not cubic like tsikourasite. It exhibits the same structure as the cubic Mo3Ni2P1.18 compound [space group F-43m, a = 10.846(2) Å] synthesized at 1350 °C. The mineral and its name have been approved by the Commission of New Minerals, Nomenclature and Classification of the International Mineralogical Association (No. 2018-156). The mineral honors Professor Basilios Tsikouras of the Universiti Brunei Darussalam. Full article
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Open AccessArticle
Spiridonovite, (Cu1-xAgx)2Te (x ≈ 0.4), a New Telluride from the Good Hope Mine, Vulcan, Colorado (U.S.A.)
Minerals 2019, 9(3), 194; https://doi.org/10.3390/min9030194 - 24 Mar 2019
Abstract
Here we describe a new mineral in the Cu-Ag-Te system, spiridonovite. The specimen was discovered in a fragment from the cameronite [ideally, Cu5-x(Cu,Ag)3+xTe10] holotype material from the Good Hope mine, Vulcan, Colorado (U.S.A.). It occurs as black [...] Read more.
Here we describe a new mineral in the Cu-Ag-Te system, spiridonovite. The specimen was discovered in a fragment from the cameronite [ideally, Cu5-x(Cu,Ag)3+xTe10] holotype material from the Good Hope mine, Vulcan, Colorado (U.S.A.). It occurs as black grains of subhedral to anhedral morphology, with a maximum size up to 65 μm, and shows black streaks. No cleavage is observed and the Vickers hardness (VHN100) is 158 kg·mm−2. Reflectance percentages in air for Rmin and Rmax are 38.1, 38.9 (471.1 nm), 36.5, 37.3 (548.3 nm), 35.8, 36.5 (586.6 nm), 34.7, 35.4 (652.3 nm). Spiridonovite has formula (Cu1.24Ag0.75)Σ1.99Te1.01, ideally (Cu1-xAgx)2Te (x ≈ 0.4). The mineral is trigonal and belongs to the space group P-3c1, with the following unit-cell parameters: a = 4.630(2) Å, c = 22.551(9) Å, V = 418.7(4) Å 3, and Z = 6. The crystal structure has been solved and refined to R1 = 0.0256. It can be described as a rhombohedrally-compressed antifluorite structure, with a rough ccp arrangement of Te atoms. It consists of two Te sites and three M (metal) sites, occupied by Cu and Ag, and is characterized by the presence of edge-sharing tetrahedra, where the four-fold coordinated M atoms lie. The mineral and its name have been approved by the Commission of New Minerals, Nomenclature and Classification of the International Mineralogical Association (No. 2018-136). Full article
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