La sénégalite,Al2 (PO4) (OH)3 · H2O,un nouveau minéral |
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| Authors: | Zdenek Johan |
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| Institution: | Zdenek Johan, Service géologique national, B.R.G.M., b.p. 6009, 45018 - Orléans, France |
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| Abstract: | Senegalite is orthorhombic, mm2, a:b:c:=1.296:1:1.007; , Z=4, Gcalc=2551; space group Pna2. The strongest lines in the powder pattern are: 5.41(7); 4.089(9); 3.834(10); 3.610(8); 2.990(9); 2.348(8); 2.070(7) 1.929(7); 1.505(7) Å. The chemical analysis: Al2O3 ? 46.23; Fe2O3 ? 0.28; P2O5 ? 31.85 H2O ? 21.00; sum 99.34, gives a formula Al2(PO4)(OH)3 · H2O. Colourless optically biaxial positive, nS: α=1.562, β=1.566, γ=1.587, plane of optical axies (001), Z=a, Y=c; 2V=53°, weak dispersion r > v. Measured density 2.552. The DTA curve shows endothermic reactions at 250, 370 and 440°C corresponding to the dehydration of mineral. Infrared spectrum indicates the presence of OH and H2O groups. Found in oxidation zone of Kouroudiako iron deposit, Senegal, associated with turquoise, augelite, wavellite and crandallite. |
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