57Fe Mossbauer study of the oxidation state of iron in stilpnomelane from granite pegmatites in Poland

Abstract

The effects of heat treatment on stilpnomelane from granite pegmatites at Zółkiewka (Lower Silesia, Poland) were studied using 57 Fe Mössbauer spectroscopy. Samples of naturally altered stilpnomelane and chlorite were also studied. The Mössbauer spectrum of an untreated sample was fitted to two Fe 2+ doublets and two Fe 3+ doublets. The Fe 2+ doublets had similar isomer shifts (1.13 and 1.16 mm/s for the octahedral M1 and M2 sites), different quadrupole splitting values (QS = 2.28 and 2.66 mm/s, respectively), and an M1:M2 area ratio of nearly 1:3. For ferric iron, the first doublet was assigned to the combined M1 + M2 + M4 octahedral positions and had IS = 0.41 and QS = 1.18 mm/s. The second doublet was assigned to the M3 site, with parameters IS = 0.36 and QS = 2.07 mm/s. This is characteristic for stilpnomelane. The oxidation of Fe 2+ is fast at low temperatures, with a maximum at 360 °C. Near 1050 °C, the stilpnomelane structure broke down completely, and the spectrum consisted of two sextets and two ferric iron doublets. The predominant phase in this new material is hematite, as represented by the two sextets. The abnormally high fractional Fe 2+ content in the altered stilpnomelane (0.70) as compared to the untreated sample (0.45) indicates that the sample was subjected to local hydrothermal processes. Nearly identical divalent iron contents and hyperfine parameters for the Fe 2+ and Fe 3+ doublets (except Fe 3+ in M3) in the altered stilpnomelane and associated chlorite strongly suggest that chlorite is transformed into stilpnomelane.

X‐ray fluorescence determination of the FeO/Fe2O3tot ratio in igneous rocks

“…Fe(II) and Fe(III) are usually differentiated by the wet chemistry technique. [3 -5] To measure Fe(II) and Fe(III) contents in separated minerals, the methods of nuclear gammaresonance (for example, refs [6,7]) and X-ray absorption near edge structure (XANES) (for example, refs [8,9]) can also be employed. The position of the peak and intensity of some characteristic lines of emission of the X-ray spectrum are affected by the chemical bonds.…”

Amphiboles and phyllosilicates in the A-type Mandira Granite Massif, Graciosa Province, SE Brazil: Textures, composition and crystallisation conditions

“…In the case of sodic amphiboles, Li contents, measured by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), were considered where available in the computed formulae. Biotite formulae and classification are according to Rieder et al (1998), whereas the schemes suggested by Zang and Fyfe (1995), Guggenheim et al (2007) and Yavuz et al (2015), and those by Hutton (1938) and Malczewski and Popiel (2008) were applied for chlorite and stilpnomelane, respectively.…”

Identification of iron-bearing minerals in basalts and pillow lavas of the Kaczawa Mountains using 57Fe Mössbauer spectroscopy

“…3), which is also identified in each basalt sample, most probably may be assigned to hornblende [3,6]. Hornblende (Ca,K,Na) 2-3 (Mg,Fe 2+ ,Fe 3+ ,Al) 5 (Si,Al) 8 O 22 (OH) 2 represents the amphiboles that is an important group of inosilicate rock-forming minerals, which occur in igneous and metamorphic rocks [2,4].…”

“…Hematite may be regarded as a secondary mineral in this type of rock and can be formed by the weathering of primary iron-bearing minerals or regional metamorphism [1,5]. 8 , a micaceous greenish mineral, is common in low-grade schist or as the alteration product of pyroxenes or amphiboles [5]. Chlorite phase was also identifi ed in the WGK sample (doublets no.…”