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.