CHAPTER III.

INVESTIGATION OF MICROSCOPIC AND OPTICAL CHARACTERS OF MINERALS. Opaque Minerals. Transparent Minerals: With transmitted light: _Form_, _Color_, _Index of Refraction and Relief_, _Becke Method_, _van der Kolk Method_, _Cleavage_, _Fracture_, _Inclusions_. With polarized transmitted light: _Pleochroism_. With crossed nicols: _Isotropic Character_, _Anisotropic Character_, _Interference Colors_, _Extinction_ and _Extinction Angles_, _Vibration Directions of Faster and Slower Rays_, _Order of Interference Color_, _Strength of Double Refraction_, _Determination of Minerals and Thickness of Section_, _Structure_. With convergent light: _Uniaxial Interference Figures_ and _Optical Character_, _Biaxial Interference Figures_ and _Optical Character_, _Determination of Axial Angle_, _Distinctions between Orthorhombic, Monoclinic and Triclinic Sections_. Resumé of Uses of Parallel and Convergent Polarized Light. 13