Amgaite, Tl 3+ 2 Te 6+ O 6 , a New Mineral from the Khokhoyskoe Gold Deposit, Eastern Siberia, Russia

• Published in: Minerals
• Main Authors: Anatoly V. Kasatkin, Galina S. Anisimova, Fabrizio Nestola, Jakub Plášil, Jiří Sejkora, Radek Škoda, Evgeniy P. Sokolov, Larisa A. Kondratieva, Veronika N. Kardashevskaia
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2022
• Subjects: amgaite; new mineral; Khokhoyskoe gold deposit; Amga river; Raman spectroscopy; chemistry; Mineralogy; QE351-399.2; Sakha; Aldan; Sakha Republic; Yakutia; Siberia
• Online Access: https://doi.org/10.3390/min12091064; https://doaj.org/article/3627169d9f124725b3f3be021ab171eb

The new mineral amgaite was discovered at the Khokhoyskoe gold deposit, 120 km W of Aldan town, Aldanskiy District, Sakha Republic (Yakutia), Eastern Siberia, Russia. Amgaite forms fine-grained colloform aggregates up to 0.05 mm across, and is often intimately intergrown with avicennite, unidentified carbonates and antimonates of Tl. Other associated minerals include gold, silver, acanthite, arsenopyrite, pyrite, berthierite, chalcocite, weissbergite, chlorargyrite, calcite, quartz, goethite etc. Amgaite is dark reddish brown to black. It has submetallic luster, black streak, brittle tenacity and conchoidal fracture. Its density calculated from the empirical formula and powder XRD data is 8.358 g/cm 3 . Its Mohs’ hardness is ca. 1.5–2. Optically, amgaite is uniaxial. In reflected light, it is gray with a bluish shade, very weakly anisotropic with rare brownish red internal reflections. Reflectance values for the four COM wavelengths [ R min , R max (%)(λ in nm)] are: 13.5, 14.2 (470); 12.7, 13.2 (546); 12.3, 12.7 (589); and 11.7, 12.3 (650). The Raman spectrum shows bands of Te–O and Tl–O bonds and confirms the absence in amgaite of H 2 O, OH – , CO 3 2– groups and B–O bonds. The chemical composition is (electron microprobe, wt.%): MgO 0.43, CaO 1.62, Fe 2 O 3 0.36, Tl 2 O 3 66.27, Sb 2 O 5 3.48, TeO 3 27.31, total 99.47. The empirical formula based on 6 O apfu is Tl 3+ 1.74 Ca 0.17 Mg 0.06 Fe 3+ 0.03 Te 6+ 0.93 Sb 5+ 0.13 O 6 . Amgaite is trigonal, space group P 321; unit-cell parameters are as follows: a = 9.0600(9), c = 4.9913(11) Å, V = 354.82(8) Å 3 , Z = 3. The strongest lines of the powder X-ray diffraction pattern [ d obs , Å ( I , %) ( hkl )] are as follows: 3.352 (100) (111), 3.063 (15) (201), 2.619 (49) (300), 2.065 (18) (221), 1.804 (28) (302), 1.697 (8) (321), 1.625 (9) (411). The crystal structure of amgaite is the same as of synthetic Tl 3+ 2 Te 6+ O 6 . The new mineral is named after the Amga River, the basin of which hosts the type locality, Khokhoyskoe occurrence. The type material is deposited ...