Elements of Optical Mineralogy: Principles and methods

absorption acute bisectrix figure albite apparent optic angle augite balsam basal sections biaxial crystals biaxial interference figures biaxial minerals birefringence calcite color curves convex side crossed nicols crystal axes difference of phase direction of vibration dispersion edge ellipsoid axes extinction angles fast ray feldspars field of view glass highest interference color hornblende hyperbolas inclined index of refraction interference figure isogyre light travels liquid measured methods mica plate mineral monoclinic negative ocular optic axis optic axis interference optic plane optic sign orthoclase orthorhombic petrographic microscope pinacoid plagioclase plane of symmetry pleochroism prism prismatic cleavage produced pyramid quadrants quartz quartz wedge refringence rhombohedron right angles rotation sections normal sensitive tint plate shown in Fig sign of elongation slow ray sulphur surface thickness thin sections tion triaxial ellipsoid triclinic twinning uniaxial uniaxial crystals uniaxial minerals velocity vertical axis vibration directions vibration planes violet light wave length wave-front wave-normal white light yellow