New Data on Fiedlerite-1A from Ancient Slags of Lavrion,Greece: Crystal Structure and Hydrogen Bonding

Doklady Earth Sciences - The crystal structure (R = 0.0750) of fiedlerite-1A Pb3Cl4F (OH) · H2O from ancient slags of Lavrion (Greece) was studied on a single crystal. The mineral is...     

Genesis and compositional characteristics of natural γ-CrOOH

Natural γ-CrOOH was first found and studied in rischorrite of the Khibina Massif, in which this mineral is associated with gonardite, natrolite, phillipsite, and saponite and usually forms microcrystallites in a matrix of amorphous CrOOH hydrogel or, more rarely, occurs as fine-crystalline, thin acicular, and lumpy aggregates of a green and emerald-green color. X-ray powder diffraction data indicate that crystalline blocks consist of a mineral with a rhombohedral unit cell, Cmcm, a = 3.86 Å, b = 12.78 Å, and c = 3.04 Å. Chromium oxyhydroxide from the Khibina Massif is isostructural with γ-CrOOH from the Iksinskoe deposit, but significantly differs from it in bearing low Al concentrations. The empirical formula of the Khibina γ-CrOOH is (Cr_0.94Mg_0.03Al_0.02Ti_0.01Fe_0.01)_1.01O(OH) · nH₂O. The Cr oxyhydroxide and associated zeolites crystallized from low-temperature hydrothermal solutions rich in Na. The most probable source of Cr for the γ-CrOOH in the Khibina Massif was titanomagnetite in xenoliths of ultrabasic rocks in the rischorrites affected by postmagmatic alterations.     

Britvinite, Pb15Mg9(Si10O28)(BO3)4(CO3)2(OH)12O2, a new mineral species from Långban, Sweden

Britvinite, a new mineral species, has been found in manganese ore at the Långban deposit, Bergslagen ore district, Filipstad, Värmland County, Sweden. Calcite, barytocalcite, brucite, cerussite, and hausmannite are associated minerals. Britvinite occurs as pale yellow to colorless transparent plates with a white streak up to 0.2 × 0.5 × 0.5 mm in size, which are flat parallel to {001}; the luster is adamantine. Thin lamellae are flexible, whereas thick ones are brittle; the Mohs hardness is 3. The cleavage is eminent parallel to {001}. The calculated density is 5.51 g/cm³. In the infrared spectrum of the new mineral, the bands of (OH)?, (CO₃)^2?, and (BO₃)^3? are recorded, whereas those corresponding to water molecules are absent. Britvinite is optically biaxial and negative, α = 1.896(2), β = 1.903(2), γ = 1.903(2), 2Vmeas = 20(10), Z≈c. Dispersion is strong, r<v. The chemical composition (electron microprobe; H₂O determined with the Alimarin method, CO₂, with selective sorption) is (wt %) 7.95 MgO, 71.92 PbO, 0.41 Al₂O₃, 12.77 SiO₂, 2.2 H₂O, 2.1 CO₂, 2.67 B₂O₃ (calculated on the basis of structural data); total 100.02. The empirical formula calculated on the basis of 59 anions (O + OH) (Z = 1) is as follows: Pb_14.75Mg_9.03Si_9.73Al_0.37O_30.76(BO₃)_3.51(CO₃)_2.18(OH)_11.7. The simplified formula (Z = 2) is Pb_{7 + x} Mg_4.5(Si₅O₁₄)(BO₃)₂(CO₃)(OH,O)₇ (x < 0.5). The crystal structure of britvinite has been studied on a single crystal at 173 K; R = 0.0547. The new mineral is triclinic, space group P $ \bar 1 Britvinite, a new mineral species, has been found in manganese ore at the L?ngban deposit, Bergslagen ore district, Filipstad, V?rmland County, Sweden. Calcite, barytocalcite, brucite, cerussite, and hausmannite are associated minerals. Britvinite occurs as pale yellow to colorless transparent plates with a white streak up to 0.2 × 0.5 × 0.5 mm in size, which are flat parallel to {001}; the luster is adamantine. Thin lamellae are flexible, whereas thick ones are brittle; the Mohs hardness is 3. The cleavage is eminent parallel to {001}. The calculated density is 5.51 g/cm³. In the infrared spectrum of the new mineral, the bands of (OH)−, (CO₃)²⁻, and (BO₃)³⁻ are recorded, whereas those corresponding to water molecules are absent. Britvinite is optically biaxial and negative, α = 1.896(2), β = 1.903(2), γ = 1.903(2), 2Vmeas = 20(10), Z≈c. Dispersion is strong, r<v. The chemical composition (electron microprobe; H₂O determined with the Alimarin method, CO₂, with selective sorption) is (wt %) 7.95 MgO, 71.92 PbO, 0.41 Al₂O₃, 12.77 SiO₂, 2.2 H₂O, 2.1 CO₂, 2.67 B₂O₃ (calculated on the basis of structural data); total 100.02. The empirical formula calculated on the basis of 59 anions (O + OH) (Z = 1) is as follows: Pb_14.75Mg_9.03Si_9.73Al_0.37O_30.76(BO₃)_3.51(CO₃)_2.18(OH)_11.7. The simplified formula (Z = 2) is Pb_{7 + x} Mg_4.5(Si₅O₁₄)(BO₃)₂(CO₃)(OH,O)₇ (x < 0.5). The crystal structure of britvinite has been studied on a single crystal at 173 K; R = 0.0547. The new mineral is triclinic, space group P ; the unit-cell dimensions are a = 9.3409(8), b = 9.3597(7), c = 18.8333(14) ?, α = 80.365(6)°, β = 75.816(6)°, γ = 59.870(5)°, V = 1378.74(19) ?³. The structure consists of alternating TOT stacks (containing octahedral brucite-like and discontinuous tetrahedral (Si₅O₁₄)_∞∞ layers) and multilayered [Pb_7.1(OH)_3.6(CO₃)(BO₃)_1.75(SiO₄)_0.25]_∞∞ blocks. The strongest reflections in the X-ray powder diffraction pattern [d, ? (I, %)(hkl)] are 18.1(100)(001), 3.39(30)(12, 14, 015), 3.02(90)(006, 130, 106, 20, 11), 2.698(70)(332, 134, 030, 1), 2.275(30)(008, 420, 424), 1.867(30)(446, 239, 2.1.10, 18), 1.766(40)(151, 31, 10, 453, 542, 512, 42), 1.519(40)(0.0.12). The mineral has been named in honor of Sergei Nikolaevich Britvin (b. 1965), a Russian mineralogist. The type material of britvinite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. The registration number is 3458/1. Original Russian Text ? N.V. Chukanov, O.V. Yakubovich, I.V. Pekov, D.I. Belakovsky, W. Massa, 2007, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2007, Pt CXXXVI, No. 6, pp. 18–25. The new mineral britvinite and its name were accepted by the Commission on New Minerals and Mineral Names, Russian Mineralogical Society, June 7, 2006, and approved by the Commission on New Minerals and Mineral Names, International Mineralogical Association, October 17, 2006.     

Karchevskyite, [Mg18Al9(OH)54][Sr2(CO3,PO4)9(H2O,H3O)11], a new mineral species of the layered double hydroxide family

Karchevskyite, a new mineral related to the family of layered double hydroxides (LDHs), has been found in the Iron open pit at the Kovdor carbonatite massif, Kola Peninsula, Russia. The mineral occurs as spherulites of up to 1.5 mm in diameter composed of thin, curved lamellae. Dolomite, magnetite, quintinite-3T, strontium carbonate, and fluorapatite are associated minerals. Karchevskyite is white in aggregates and colorless in separate platelets. Its luster is vitreous with a pearly shine on the cleavage surface. The new mineral is nonfluorescent. The Mohs hardness is 2. The cleavage is eminent (micalike), parallel to {001}. The measured density is 2.21(2) g/cm³, and the calculated value is 2.18(1) g/cm³. Karchevskyite is colorless and nonpleochroic in immersion liquids. It is uniaxial, negative, ω = 1.542(2), and ? = 1.534(2). The chemical composition (electron microprobe, average of ten point analyses, standard deviation in parentheses, wt %) is as follows: 29.7(1.1) MgO, 18.3(0.7) Al₂O₃, 7.4(0.4) SrO, 0.2(0.1) CaO, 1.3(0.2) P₂O₅, 14.5(0.4) CO₂, and 28.6 H₂O (estimated by difference); the total is 100. The empirical formula calculated on the basis of nine Al atoms is Mg_18.00Al_9.00(OH)_54.00(Sr_1.79Mg_0.48Ca_0.09)_2.36 (Ca₃)_8.26(PO₄)_0.46(H₂O)_6.54(H₃O)_4.18. The idealized formula is [Mg₁₈Al₉(OH)₅₄][Sr₂(CO₃, PO₄)₉(H₂O, H₃O)₁₁]. The new mineral slowly dissolves in 10% HCl with weak effervescence. Karchevskyite is trigonal; possible space groups are P3, P3, P $ \overline 3 Karchevskyite, a new mineral related to the family of layered double hydroxides (LDHs), has been found in the Iron open pit at the Kovdor carbonatite massif, Kola Peninsula, Russia. The mineral occurs as spherulites of up to 1.5 mm in diameter composed of thin, curved lamellae. Dolomite, magnetite, quintinite-3T, strontium carbonate, and fluorapatite are associated minerals. Karchevskyite is white in aggregates and colorless in separate platelets. Its luster is vitreous with a pearly shine on the cleavage surface. The new mineral is nonfluorescent. The Mohs hardness is 2. The cleavage is eminent (micalike), parallel to {001}. The measured density is 2.21(2) g/cm³, and the calculated value is 2.18(1) g/cm³. Karchevskyite is colorless and nonpleochroic in immersion liquids. It is uniaxial, negative, ω = 1.542(2), and ɛ = 1.534(2). The chemical composition (electron microprobe, average of ten point analyses, standard deviation in parentheses, wt %) is as follows: 29.7(1.1) MgO, 18.3(0.7) Al₂O₃, 7.4(0.4) SrO, 0.2(0.1) CaO, 1.3(0.2) P₂O₅, 14.5(0.4) CO₂, and 28.6 H₂O (estimated by difference); the total is 100. The empirical formula calculated on the basis of nine Al atoms is Mg_18.00Al_9.00(OH)_54.00(Sr_1.79Mg_0.48Ca_0.09)_2.36 (Ca₃)_8.26(PO₄)_0.46(H₂O)_6.54(H₃O)_4.18. The idealized formula is [Mg₁₈Al₉(OH)₅₄][Sr₂(CO₃, PO₄)₉(H₂O, H₃O)₁₁]. The new mineral slowly dissolves in 10% HCl with weak effervescence. Karchevskyite is trigonal; possible space groups are P3, P3, P 1m, P31m, P312, P312, P3m1, or P3m1; unit-cell dimensions are a = 16.055(6), c = 25.66(1) ?, V = 5728(7) ?³, Z = 3. The strongest reflections in the X-ray powder diffraction pattern [d, (I, %)(hkl)] are: 8.52(10)(003), 6.41(4)(004), 5.13(3)(005), 4.27(6)(006), 3.665(9)(007), 3.547(9)(107), 3.081(6)(315). Wavenumbers of absorption bands in the infrared spectrum of the new mineral are (cm⁻¹; s is shoulder): 3470, 3420s, 3035, 2960s, 1650, 1426, 1366, 1024, 937, 860, 779, 678, 615s, 553, 449, 386. Results of thermogravimetric analysis: total weight loss is 42.0 wt %, with three stages of loss: 12.2%, maximum rate at 230°C; 6.1%, maximum rate at 320°C; and 23.7%, maximum rate at 440°C. Karchevskyite is a late-stage hydrothermal mineral. The mineral is named in memory of Russian mineralogist Pavel Karchevsky (1976–2002), who made a significant contribution to the study of carbonatites. The type material of karchevskyite is deposited at the Mineralogical Museum, Division of Mineralogy, St. Petersburg State University, and the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. Original Russian Text ? S.N. Britvin, N.V. Chukanov, G.K. Bekenova, M.A. Yagovkina, A.V. Antonov, A.N. Bogdanova, N.I. Krasnova, 2007, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2007, No. 5, pp. 44–56. The new mineral karchevskyite and its name accepted by the Commission on New Minerals and Mineral Names, Russian Mineralogical Society, March 21, 2005. Approved by the Commission on New Minerals and Mineral Names, International Mineralogical Association, June 30, 2005.     

Middendorfite,K<Subscript>3</Subscript>Na<Subscript>2</Subscript>Mn<Subscript>5</Subscript>Si<Subscript>12</Subscript>(O,OH)<Subscript>36</Subscript> · 2H<Subscript>2</Subscript>O,a new mineral species from the Khibiny pluton,Kola Peninsula

Middendorfite, a new mineral species, has been found in a hydrothermal assemblage in Hilairite hyperperalkaline pegmatite at the Kirovsky Mine, Mount Kukisvumchorr apatite deposit, Khibiny alkaline pluton, Kola Peninsula, Russia. Microcline, sodalite, cancrisilite, aegirine, calcite, natrolite, fluorite, narsarsukite, labuntsovite-Mn, mangan-neptunite, and donnayite are associated minerals. Middendorfite occurs as rhombshaped lamellar and tabular crystals up to 0.1 × 0.2 × 0.4 mm in size, which are combined in worm-and fanlike segregations up to 1 mm in size. The color is dark to bright orange, with a yellowish streak and vitreous luster. The mineral is transparent. The cleavage (001) is perfect, micalike; the fracture is scaly; flakes are flexible but not elastic. The Mohs hardness is 3 to 3.5. Density is 2.60 g/cm³ (meas.) and 2.65 g/cm³ (calc.). Middendorfite is biaxial (?), α = 1.534, β = 1.562, and γ = 1.563; 2V (meas.) = 10°. The mineral is pleochroic strongly from yellowish to colorless on X through brown on Y and to deep brown on Z. Optical orientation: X = c. The chemical composition (electron microprobe, H₂O determined with Penfield method) is as follows (wt %): 4.55 Na₂O, 10.16 K₂O, 0.11 CaO, 0.18 MgO, 24.88 MnO, 0.68 FeO, 0.15 ZnO, 0.20 Al₂O₃, 50.87 SiO₂, 0.17 TiO₂, 0.23 F, 7.73 H₂O; ?O=F₂?0.10, total is 99.81. The empirical formula calculated on the basis of (Si,Al)₁₂(O,OH,F)₃₆ is K_3.04(Na_2.07Ca_0.03)_Σ2.10(Mn_4.95Fe_0.13Mg_0.06Ti_0.03Zn_0.03)_Σ5.20(Si_11.94Al_0.06)_Σ12O_27.57(OH)_8.26F_0.17 · 1.92H₂O. The simplified formula is K₃Na₂Mn₅Si₁₂(O,OH)₃₆ · 2H₂O. Middenforite is monoclinic, space group: P2₁/m or P2₁. The unit cell dimensions are a = 12.55, b = 5.721, c = 26.86 Å; β = 114.04°, V = 1761 ų, Z = 2. The strongest lines in the X-ray powder pattern [d, Å, (I)(hkl)] are: 12.28(100)(002), 4.31(81)(11\(\overline 4 \)), 3.555(62)(301, 212), 3.063(52)(008, 31\(\overline 6 \)), 2.840(90)(312, 021, 30\(\overline 9 \)), 2.634(88)(21\(\overline 9 \), 1.0.\(\overline 1 \)0, 12\(\overline 4 \)), 2.366(76)(22\(\overline 6 \), 3.1.\(\overline 1 \)0, 32\(\overline 3 \)), 2.109(54)(42–33, 42–44, 51\(\overline 9 \), 414), 1.669(64)(2.2.\(\overline 1 \)3, 3.2.\(\overline 1 \)3, 62\(\overline 3 \), 6.1.\(\overline 1 \)3), 1.614(56)(5.0.\(\overline 1 \)6, 137, 333, 71\(\overline 1 \)). The infrared spectrum is given. Middendorfite is a phyllosilicate related to bannisterite, parsenttensite, and the minerals of the ganophyllite and stilpnomelane groups. The new mineral is named in memory of A.F. von Middendorff (1815–1894), an outstanding scientist, who carried out the first mineralogical investigations in the Khibiny pluton. The type material of middenforite has been deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.     

Zinclipscombite,ZnFe<Stack><Subscript>2</Subscript><Superscript>3+</Superscript></Stack>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>(OH)<Subscript>2</Subscript>, a new mineral species

Zinclipscombite, a new mineral species, has been found together with apophyllite, quartz, barite, jarosite, plumbojarosite, turquoise, and calcite at the Silver Coin mine, Edna Mountains, Valmy, Humboldt County, Nevada, United States. The new mineral forms spheroidal, fibrous segregations; the thickness of the fibers, which extend along the c axis, reaches 20 μm, and the diameter of spherulites is up to 2.5 mm. The color is dark green to brown with a light green to beige streak and a vitreous luster. The mineral is translucent. The Mohs hardness is 5. Zinclipscombite is brittle; cleavage is not observed; fracture is uneven. The density is 3.65(4) g/cm³ measured by hydrostatic weighing and 3.727 g/cm³ calculated from X-ray powder data. The frequencies of absorption bands in the infrared spectrum of zinclipscombite are (cm^?1; the frequencies of the strongest bands are underlined; sh, shoulder; w, weak band) 3535, 3330sh, 3260, 1625w, 1530w, 1068, 1047, 1022, 970sh, 768w, 684w, 609, 502, and 460. The Mössbauer spectrum of zinclipscombite contains only a doublet corresponding to Fe³⁺ with sixfold coordination and a quadrupole splitting of 0.562 mm/s; Fe²⁺ is absent. The mineral is optically uniaxial and positive, ω = 1.755(5), ? = 1.795(5). Zinclipscombite is pleochroic, from bright green to blue-green on X and light greenish brown on Z (X > Z). Chemical composition (electron microprobe, average of five point analyses, wt %): CaO 0.30, ZnO 15.90, Al₂O₃ 4.77, Fe₂O₃ 35.14, P₂O₅ 33.86, As₂O₅ 4.05, H₂O (determined by the Penfield method) 4.94, total 98.96. The empirical formula calculated on the basis of (PO₄,AsO₄)₂ is (Zn_0.76Ca_0.02)_Σ0.78(Fe _1.72 ³⁺ Al_0.36)_Σ2.08[(PO₄)_1.86(AsO₄)_0.14]_Σ2.00(OH)_{1. 80} · 0.17H₂O. The simplified formula is ZnFe ₂ ³⁺ (PO₄)₂(OH)₂. Zinclipscombite is tetragonal, space group P4₃2₁2 or P4₁2₁2; a = 7.242(2) Å, c = 13.125(5) Å, V = 688.4(5) ų, Z = 4. The strongest reflections in the X-ray powder diffraction pattern (d, (I, %) ((hkl)) are 4.79(80)(111), 3.32(100)(113), 3.21(60)(210), 2.602(45)(213), 2.299(40)(214), 2.049(40)(106), 1.663(45)(226), 1.605(50)(421, 108). Zinclipscombite is an analogue of lipscombite, Fe²⁺Fe ₂ ³⁺ (PO₄)₂(OH)₂ (tetragonal), with Zn instead of Fe²⁺. The mineral is named for its chemical composition, the Zn-dominant analogue of lipscombite. The type material of zinclipscombite is deposited in the Mineralogical Collection of the Technische Universität Bergakademie Freiberg, Germany.     

Attikaite,Ca<Subscript>3</Subscript>Cu<Subscript>2</Subscript>Al<Subscript>2</Subscript>(AsO<Subscript>4</Subscript>)<Subscript>4</Subscript>(OH)<Subscript>4</Subscript> · 2H<Subscript>2</Subscript>O,a new mineral species

Attikaite, a new mineral species, has been found together with arsenocrandalite, arsenogoyazite, conichalcite, olivenite, philipsbornite, azurite, malachite, carminite, beudantite, goethite, quartz, and allophane at the Christina Mine No. 132, Kamareza, Lavrion District, Attiki Prefecture (Attika), Greece. The mineral is named after the type locality. It forms spheroidal segregations (up to 0.3 mm in diameter) consisting of thin flexible crystals up to 3 × 20 × 80 μm in size. Its color is light blue to greenish blue, with a pale blue streak. The Mohs’ hardness is 2 to 2.5. The cleavage is eminent mica-like parallel to {001}. The density is 3.2(2) g/cm³ (measured in heavy liquids) and 3.356 g/cm³ (calculated). The wave numbers of the absorption bands in the infrared spectrum of attikaite are (cm^?1; sh is shoulder; w is a weak band): 3525sh, 3425, 3180, 1642, 1120w, 1070w, 1035w, 900sh, 874, 833, 820, 690w, 645w, 600sh, 555, 486, 458, and 397. Attikaite is optically biaxial, negative, α = 1.642(2), β = γ = 1.644(2) (X = c) 2V _means = 10(8)°, and 2V _calc = 0°. The new mineral is microscopically colorless and nonpleochroic. The chemical composition (electron microprobe, average over 4 point analyses, wt %) is: 0.17 MgO, 17.48 CaO, 0.12 FeO, 16.28 CuO, 10.61 Al₂O₃, 0.89 P₂O₅, 45.45 As₂O₅, 1.39 SO₃, and H₂O (by difference) 7.61, where the total is 100.00. The empirical formula calculated on the basis of (O,OH,H₂O)₂₂ is: Ca_2.94Cu _1.93 ²⁺ Al_1.97Mg_0.04Fe _0.02 ²⁺ [(As_3.74S_0.16P_0.12)_Σ4.02O_16.08](OH)_3.87 · 2.05H₂ O. The simplified formula is Ca₃Cu₂Al₂(AsO₄)₄(OH)₄ · 2H₂O. Attikaite is orthorhombic, space group Pban, Pbam or Pba2; the unit-cell dimensions are a = 10.01(1), b = 8.199(5), c = 22.78(1) Å, V = 1870(3) ų, and Z = 4. In the result of the ignition of attikaite for 30 to 35 min at 128–140°, the H₂O bands in the IR spectrum disappear, while the OH-group band is not modified; the weight loss is 4.3%, which approximately corresponds to two H₂O molecules per formula; and parameter c decreases from 22.78 to 18.77 Å. The strongest reflections in the X-ray powder diffraction pattern [d, Å (I, %)((hkl)] are: 22.8(100)(001), 11.36(60)(002), 5.01(90)(200), 3.38(5)(123, 205), 2.780(70)(026), 2.682(30)(126), 2.503(50)(400), 2.292(20)(404). The type material of attikaite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. The registration number is 3435/1.     

Thorium mineralization in hyperalkaline pegmatites and hydrothermalites of the Lovozero pluton,Kola Peninsula

The Lovozero pluton (Kola Peninsula, Russia) is an unique object from the standpoint of the abundance, diversity, and originality of Th mineralization. In contrast to other igneous rocks and to such chemical elements as Ca, REE, U, and Na, Th in the hyperalkaline pegmatites and hydrothermalites of the Lovozero pluton commonly occurs as its own mineral phases. Umbozerite Na₃Sr₄Th(Mn,Zn,Fe,Mg)[Si₈O₂₄](OH) (7 samples), Ti-Th silicate Na_0–7Sr_0–1ThTi_1–2Si₈O_22–23(OH) · nH₂O (8 samples), Na-Th silicate (Na,K)₄Th₃[Si₈(O,OH)₂₄] · nH₂O (6 samples), thorite (2 samples), steenstrupine-(Ce)-thorosteenstrupine series minerals (5 samples), and Th phosphate (Th,Na,K,Ca,Mg,U,Sr,Ba)[(P,Si, Al)₁O₄] · nH₂O (1 sample) were investigated in this study. Ti-Th silicates and Th phosphate have been described for the first time. All of the above-mentioned minerals have been examined with electron microprobe, IR spectroscopy, powder diffraction, thermogravimetric and optical methods. High-Th minerals such as steenstrupine, umbozerite, Th phosphate, and Na-Th silicates crystallized mainly during the ussingite stage of the pegmatite-forming process. At the early hydrothermal high-alkaline stage, steenstrupine was replaced with REE and Th aggregates (belovite, vitusite, seidite, Na-Th silicates, Ti-Th silicates, etc.). Thorite, Ti-Th silicates, and minerals of the rhabdophane and monazite groups were formed at the late hydrothermal low-alkaline stage. Despite the metamict features of almost all samples, stoichiometric ratios of cations in umbozerites and Ti-Th silicates remain stable. Clear relationships have been revealed between umbozerites and Ti-Th silicates, on the one hand, and seidite-(Ce), a Ti-silicate that has a zeolite-like structure, on the other. This implies that, under certain conditions, these minerals may be regarded as potential suppliers of Th to the environment due to the leaching of Th from zeolite channels.