The tunnel-structure manganese oxide minerals, hollandite (Apuí, Amazonas state, Brazil, area in prospection) and cryptomelane (Urucum, Mato do Sul Grosso state, Brazil) were isolated and characterized chemical, mineralogical, thermal and morphologically. The following techniques were employed: scanning electron microscopy-EDS, thermal analysis (DTA-TG), X-ray diffraction with
continuous-heating. The empirical formula, were calculated on the basis 16 oxygen gave as (Ba0.18K0.12Ca0.02Pb0.04) 0.76(Mn6.34Al 0.61Si0.25Fe0.24Ti0.08)7.54O160.4H2O for hollandite and (K0.9Na0.04Ca0.03Sr0.04)1.04(Mn7.38Fe0.28Al0.27Si0.08)8O16 for cryptomelane. The SEM
investigations allowed the differentiation of the morphologies for hollandite and cryptomelane. The minerals were thermally treated among 100-900 ºC and X-ray diffraction patterns in situ were collected. The analysis of X-ray diffractions experiments showed that a hollandite-crytomelane mineral has a thermal stability up to 900 ºC.
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