Lobanovite, K2Na(Fe2+ Mg2Na)Ti2(Si4O12)2O2(OH)4, is a new mineral of the astrophyllite supergroup from Mt. Yukspor, the Khibiny alkaline massif, Kola Peninsula Russia. It has been previously known under the following names: monoclinic astrophyllite, magnesium astrophyllite, magnesiumastrophyllite and magnesioastrophyllite but has never been formally proposed and approved as a valid mineral species by the CNMNC-IMA. It has now been revalidated and named lobanovite after Dr. Konstantin V. Lobanov, a prominent Russian ore geologist who worked in Kola Peninsula for more than forty years (Nomenclature voting proposal 15-B). Lobanovite has been described from pegmatitic cavities on Mt. Yukspor where it occurs as elongated bladed crystals, up to 0.04 mm wide and 0.2 mm long, with straw yellow to orange colour. Associated minerals are shcherbakovite, lamprophyllite, delindeite, wadeite, umbite and kostylevite. Lobanovite is biaxial (–) with refractive indices (lambda = 589 nm) alpha = 1.658, betacalc. = 1.687, gamma = 1.710; 2Vmeas. = 81.5–83°. Lobanovite is monoclinic, space group C2/m, a 5.3327(2), b23.1535(9), c 10.3775(4) Å,beta 99.615(1)°, V 1263.3(1) Å3, Z = 2. The six strongest reflections in the X-ray powder diffraction data [d (Å), I, (hkl)] are: 3.38, 100, (003); 2.548, 90, (063); 10.1, 80, (001); 3.80, 60, (042,131); 3.079, 50, (132,062); 2.763, 90, (⎯171). The chemical composition of lobanovite was determined by electron-microprobe analysis and the empirical formula (K1.97Ba0.01)Σ1.98 (Na0.65Ca0.14)Σ0.79 (Fe2+3.18Mg2.02Na1.00Mn0.72)Σ6.92(Ti1.99 Nb0.06)Σ2.05[(Si8.01 Al0.06)Σ8.07O24]O2(OH)4.03F0.19 was calculated on the basis of 30.2 (O + OH + F) anions, with H2O calculated from structure refinement, Dcalc. = 3.161 g cm–3. In the structure of lobanovite, the main structural unit is the HOH block, which consists of one close-packed O (Octahedral) and two H (Heteropolyhedral) sheets. The M(1–4) octahedra form the O sheet and the T4O12 astrophyllite ribbons and [5]-coordinated Ti-dominant D polyhedra link through common vertices to form the H sheet. The HOH blocks repeat along [001], and K and Na atoms occur at the interstitial A and B sites. The simplified and endmember formulae of lobanovite are K2Na[(Fe2+,Mn)4Mg2Na]Ti2(Si4O12)2O2(OH)4 and K2Na(Fe2+4Mg2Na)Ti2(Si4O12)2O2(OH)4, respectively.

Lobanovite, K2Na(Fe2+4Mg2Na)Ti2(Si4O12)2O2(OH)4, a new mineral of the astrophyllite supergroup and its relation to magnesioastrophyllite

CAMARA ARTIGAS, Fernando;
2017-01-01

Abstract

Lobanovite, K2Na(Fe2+ Mg2Na)Ti2(Si4O12)2O2(OH)4, is a new mineral of the astrophyllite supergroup from Mt. Yukspor, the Khibiny alkaline massif, Kola Peninsula Russia. It has been previously known under the following names: monoclinic astrophyllite, magnesium astrophyllite, magnesiumastrophyllite and magnesioastrophyllite but has never been formally proposed and approved as a valid mineral species by the CNMNC-IMA. It has now been revalidated and named lobanovite after Dr. Konstantin V. Lobanov, a prominent Russian ore geologist who worked in Kola Peninsula for more than forty years (Nomenclature voting proposal 15-B). Lobanovite has been described from pegmatitic cavities on Mt. Yukspor where it occurs as elongated bladed crystals, up to 0.04 mm wide and 0.2 mm long, with straw yellow to orange colour. Associated minerals are shcherbakovite, lamprophyllite, delindeite, wadeite, umbite and kostylevite. Lobanovite is biaxial (–) with refractive indices (lambda = 589 nm) alpha = 1.658, betacalc. = 1.687, gamma = 1.710; 2Vmeas. = 81.5–83°. Lobanovite is monoclinic, space group C2/m, a 5.3327(2), b23.1535(9), c 10.3775(4) Å,beta 99.615(1)°, V 1263.3(1) Å3, Z = 2. The six strongest reflections in the X-ray powder diffraction data [d (Å), I, (hkl)] are: 3.38, 100, (003); 2.548, 90, (063); 10.1, 80, (001); 3.80, 60, (042,131); 3.079, 50, (132,062); 2.763, 90, (⎯171). The chemical composition of lobanovite was determined by electron-microprobe analysis and the empirical formula (K1.97Ba0.01)Σ1.98 (Na0.65Ca0.14)Σ0.79 (Fe2+3.18Mg2.02Na1.00Mn0.72)Σ6.92(Ti1.99 Nb0.06)Σ2.05[(Si8.01 Al0.06)Σ8.07O24]O2(OH)4.03F0.19 was calculated on the basis of 30.2 (O + OH + F) anions, with H2O calculated from structure refinement, Dcalc. = 3.161 g cm–3. In the structure of lobanovite, the main structural unit is the HOH block, which consists of one close-packed O (Octahedral) and two H (Heteropolyhedral) sheets. The M(1–4) octahedra form the O sheet and the T4O12 astrophyllite ribbons and [5]-coordinated Ti-dominant D polyhedra link through common vertices to form the H sheet. The HOH blocks repeat along [001], and K and Na atoms occur at the interstitial A and B sites. The simplified and endmember formulae of lobanovite are K2Na[(Fe2+,Mn)4Mg2Na]Ti2(Si4O12)2O2(OH)4 and K2Na(Fe2+4Mg2Na)Ti2(Si4O12)2O2(OH)4, respectively.
2017
81
1
175
181
lobanovite, magnesiumastrophyllite, astrophyllite supergroup, chemical composition, crystal-structure refinement
Sokolova, Elena; Cámara, Fernando; Hawthorne, Frank C; Semenov, E.I; Ciriotti, Marco E
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/1557068
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