Khibiny Alkaline Massif Research Articles

Crystal structure and microtwinning of a calcium-rich analogue of labuntsovite

The structure of a new representative of the labuntsovite family, which was found in the Khibiny alkaline massif (the Kola Peninsula), was established by the method of X-ray diffraction analysis. The unit-cell parameters are a = 14.365(7) A, b = 13.887(7) A, c = 7.814(2) A, β = 117.36(5)°, sp. gr. Cm, R aniso = 0.058, 1385 F > 4σ(F). The mineral differs from other members of the family by the absence of Na-atoms and the high Ca-content. The Ca-polyhedron is reduced to a seven-vertex polyhedron (the average Ca-O distance is 2.48 A) compared to the eight-vertex Na-polyhedron (the average Na-O distance is 2.57 A). The structure channels are orderly occupied, thus lowering the symmetry to Cm.

Refinement of the crystal structure of sanidine-like feldspar

The crystal structure of sanidine-like feldspar of the composition KAlSi3O8 from the Khibiny alkaline massif (the Kola Peninsula) has been refined (X-ray diffraction analysis; automated Syntex \(P\bar 1\) diffractometer; 2θ: θ scanning technique; 2320 reflections; R(hkl) = 0.0409; anisotropic refinement; AREN program package). The data obtained for KAlSi3O8 are: a = 8.615(9), b = 13.030(7), c = 7.200(5) A, α = 89.99(5)°, β = 116.01(6)°, γ = 89.98(7)°, Z = 4, sp. gr. \(C\bar 1\). Microtwinning revealed in the crystal structure of the mineral explains the simultaneous existence of two structural-optical types in one sample—“high” and “low” sanidines.

3H- 3He dating: A case for mixing of young and old groundwaters

3He 4He and 20Ne 4He ratios were measured in shallow underground waters (opened by water-supplying wells) of the Large Vud-Javr intramountain artesian basin in the Khibiny alkaline massif, the Kola Peninsula. The ratios vary from 1.321 × 10 −6 to 2.065 × 10 −6 and from 1.412 to 2.941, respectively, and a well-defined correlation is observed between them. Both these ratios in aquifers are known to be time-dependent, the former increases with time due to accumulation of 3He, produced in waters by 3H β-decay; the latter decreases due to migration of helium from water-bearing rocks into the waters. The correlation is interpreted as a result of the mixing of two different types of waters. The approximation line enables us to estimate the isotopic ratios for the endmembers participating in the mixing and the mean residence time (τ) of tritigenic helium-3 in the water: 1. (1) 3He 4He = 3.655 × 10 −6 , 20Ne 4He = 4.03 , and taking into consideration 3H concentrations in the well waters, 3H = 31.1 TU (practically the same for all samples), τ = 15.8 ± 1.5 years for the young water; 2. (2) 3He 4He = 0.20 × 10 −6 , 20Ne 4He = 0.18 and T = 0.11 Ma for the old one, the contribution of the old water being less than 10%. In one well a considerable contribution of modern-day meteoric water, about 16%, is observed.

Dependence of Nonlinear Optical Properties of Nepheline on its Chemical Composition and Structural State (Khibiny Alkaline Massif)

Dependence of Nonlinear Optical Properties of Nepheline on its Chemical Composition and Structural State (Khibiny Alkaline Massif)