Synthesis and absorption spectra of large homogeneous single crystals of forsterite doped with manganese

In synthetic single crystals of the olivine group, a strong compositional zoning along the growth direction has often been observed. Here we have synthesized large homogeneous single crystals of forsterite doped with manganese (50 mm×150–200 mm) by the Czochralski method using a large volume crucible, at ∼1950 °C in an N2 atmosphere. The size of the crystals in this study is the largest reported. The homogeneous parts of as-grown crystals with the compositions of (Mn0.004Mg0.996)2SiO4 and (Mn0.011Mg0.989)2SiO4 are as large as 20×20×50 mm3 [x=0.0040±0.0004 in (MnxMg1−x)2SiO4] and 12×12×30 mm3 [x=0.011±0.001], respectively. The crystals were prepared to allow for accurate measurements of physical properties and their anisotropies of pure Mn bearing forsterite, to extract the effect of Mn itself, ultimately for the study of the Earth's mantle. The polarized absorption spectra were measured for an evidence of measured anisotropy, and the clear pleochroism was observed.