Study Of Mineralogical Characteristics And High Pressure Structure Of Ilvaite

The mineral ilvaite is a mixed-valence iron island sorosilicate.In this thesis,the mineralogical characteristics of sample ilvaite is studied by means of large-scaleinstruments such as electron probe microanalysis?EPMA?,X-ray diffraction analysis?XRD?,Raman spectroscopy and infrared spectroscopy?IR?.In addition,the in situ high pressure powder X-ray diffraction experiments were carried out to study the structural changes of ilvaite under high pressure.The EPMA data shows that the chemical formula of the ilvaite sample is(Ca_0.98Mn_0.02)(Fe²⁺_1.66Fe³⁺_1.20Mn²⁺_0.2Mg²⁺_0.03)[Si_1.90O₇]O?OH?.From X-ray single crystal diffraction data,it is found that the ilvaite is monoclinic system,with the space group P2₁/a.The date of cell parameter of this ilvaite is a=13.0084?,b=8.8254?,c=5.8470?,V=671.26?³,and?=90.13°.The atomic contents,estimated by GHOSE value,there are0.63Fe²⁺and 0.37Fe³⁺in the M11 site,and 0.37Fe²⁺and 0.63Fe³⁺in the M12 site.It can be calculated that the order degree of ilvaite is 26%.The Raman spectra collected in our experiments have high ignal-to-noise ration,which may be caused by its black color.Infrared spectra show that the sample has avibration absorption peak of hydroxyl around 2974.01cm^-1.1200-800 cm^-11 peak is caused by the stretching vibration of Si-O and Si-O-Si.The peaks around 903.95 cm^-11 and 820.75cm^-1 reflect the crystal structure of hexahedron sorosilicate.In situ high pressure X-ray diffraction experiments show that the cell parameter of ilvaite decreases gradually during being compressed to 15.2GPa.The compressibility of the three crystal axes shows the anisotropy?_c>?_b>?_a,which means that the c-axis is the easiest and the a-axis is the most difficult to be compressed in the experimental pressure range.We deduced the sample's structure changed from monoclinic to orthorhombic at3.2GPa,and this is described as displacement phase transformation.Another structural phase transformation took place at 10.2GPa.The Birch-murnaghan equation of state was used to fitted the isothermal pressure-volume data.The fitted results indicate that the unit-cell volume at ambient pressure V₀ is 669.397?2??³ and the bulk modulus K₀ is151.48?4?GPa by fixing its first derivative K'at 4.