Amphiboles of predominantly tremolite composition have been synthesized at 670-800 degrees C and 200-700 MPa in the system CaO-MgO-SiO2-H2O. The tremolite crystals were large enough to be analyzed by electron microprobe. The run products were also studied by scanning electron microscopy, high resolution electron microscopy, X-ray diffraction (Rietveld analysis) and IR spectroscopy. The electron microprobe analyses resulted in average compositions between tr(87)cum(13) and tr(99)cum(1). The cummingtonite contents determined by electron microprobe varied by up to +/-7 mol% within each run. Investigations using high resolution electron microscopy revealed that the tremolite-cummingtonite solid solutions were highly ordered and chain multiplicity faults were rare. Although the lattice parameters a, b and beta are expected to be a function of the cummingtonite content, no correlations were observed between the compositions derived by electron microprobe and the lattice parameters. The energy and absorbance of the OH stretching vibration is a function of M4 site occupancy. Therefore, the cummingtonite content was determined precisely by IR spectroscopy. At least 3 different bands at distinct energies were identified: 3674.6 cm(-1) for the CaCa-CaCa and 3669.3 and 3672.2 cm(-1) for the MgCa-CaCa and CaCa-MgCa configurations, respectively. The relative integral absorbances showed that all synthesized amphiboles had cummingtonite contents lower than 6 mol%. In some cases nearly pure tremolite was synthesized (tr(99)cum(1)). This amount is considerably less than the 10 mol% cummingtonite content (tr(90)cum(10)) often claimed for synthetic tremolite. The compositions derived by IR spectroscopy correlate with the lattice parameters. Using these correlations the lattice parameters of pure tremolite were extrapolated to be a = 9.8353(18) Angstrom, b = 18.0562(14) Angstrom, c = 5.2768(6) Angstrom, beta = 104.74(2)degrees, V = 906.3(2) Angstrom(3).

Spectroscopic methods provide information about the local structure of minerals. The methods do not depend on long-range periodicity or crystallinity. The geometric arrangement of atoms in a mineral phase is only one aspect of its constitution. Its vibrational characteristic, electronic structure and magnetic properties are of greatest importance when we consider the behaviour of minerals in dynamic processes. The characterisation of the structural and physico-chemical properties of a mineral requires the application of several complementary spectroscopic techniques. However, it is one of the main aims of this School to demonstrate that different spectroscopic methods work on the same basic principles. Spectroscopic techniques represent an extremely rapidly evolving area of mineralogy and many recent research efforts are similar to those in materials science, solid state physics and chemistry. Applications to different materials of geoscientific relevance have expanded by the development of microspectroscopic techniques and by in situ measurements at low- to high-temperature and high-pressure conditions.