absorption spectrum aluminium baddeleyite calcium ceramic cerium chemical vapor deposition chromium conchoidal fracture copper crucible crystal crystallography diamond diamond-like carbon diamond simulant dopant erbium france gadolinium gadolinium gallium garnet gallium garnet gemology gemstone germany gold iridescence lebedev physical institute loupe luminescence metal metamictization microscope mineralogy mohs scale of mineral hardness moscow neodymium oxide quartz raman spectroscopy rare earth element refractive index refractory rutile silicate skull crucible soviet union specific gravity strontium titanate synthetic diamond thermal conductivity titanium topaz trigon yttria-stabilized zirconia yttrium zircon zirconium