ISSN:
1432-0967
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract Kanonaite forms rare porphyroblasts up to 12mm long in a gahnite— Mg-chlorite — coronadite — quartz schist occurring near Kanona, Zambia. The composition is (microprobe analysis): SiO2 32.2, Al2O3 33.9, Mn as Mn2O3 32.2, Fe2O3 0.66, ZnO 0.13, MgO 0.04, BaO 0.04, TiO2 0.01, CaO 0.01, PbO 0.01, CuO 0.01, total 99.21, corresponding to $$\left( {{\text{Mn}}_{{\text{0}}{\text{.76}}}^{{\text{3 + }}} {\text{Al}}_{{\text{0}}{\text{.23}}} {\text{Fe}}_{{\text{0}}{\text{.015}}}^{{\text{3 + }}} } \right)_{1.005}^{\left[ 6 \right]} {\text{AL}}_{1.00}^{\left[ 5 \right]} \left[ {{\text{O}}_{{\text{1}}{\text{.00}}} |{\text{Si}}_{{\text{0}}{\text{.99}}} {\text{O}}_{{\text{4}}{\text{.00}}} } \right]$$ The mineral is greenish black, strongly pleochroic with X(∥a) yellow green, Y(∥b) bluish green, Z(∥c) deep golden yellow, biaxial positive, with 2V = 53°(3°), α = 1.702, β = 1.730, γ = 1.823. Vickers microhardness (100 gram load) ranges between 906 and 1017kp/mm2. The structure is orthorhombic, isotypic with andalusite, space group Pnnm, a = 0.7953(2), b = 0.8038(2), c = 0.5619(2) nm, V = 0.3592(1) nm3, a/b = 0.9895(3), c/b = 0.6990(3), S.G.(x) = 3.395 g/cm3, Z = 4. The strongest X-ray powder lines are (d in nm, I, hkl):0.5669, 100, 110; 0.4590, 75, 011 and 101; 0.3577, 90, 120 and 210; 0.2827, 94, 220; 0.2517, 90, 310 and 112; 0.2212, 83, 320, 122 and 212. Comparison of the intensities of 373 observed X-ray reflections with those calculated for several models of Mn3+-distribution indicates octahedral coordination of all or most of the manganese present. Interpretation of magnetic measurements (μeff = 3.15B.M. per Mn atom at 25 ° C) indirectly supports octahedral coordination of Mn3+. The name of the mineral is for Kanona, a town near the type locality. The name is proposed for the end member Mn3+ [6]Al[5][O¦SiO4] and for members of the solid-solution series towards andalusite with octahedral Mn3+〉Al. The presently described mineral may be referred to as aluminian kanonaite.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00373417
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