EARTHSC 1108 Lecture Notes - Lecture 3: Orthorhombic Crystal System, Iridescence, Incandescent Light Bulb
1 Dec 2016
School
Department
Course
Professor
Document Summary
Light travels differently along different crystal axes. Stone must be dr to display true pleochroism: orthorhombic, monoclinic, triclinic. Some gems can be trichroic rare and 27055$ Pleochroic" technically means trichroic": but few gems with trichroism clear enough to see. In practice, pleochroism" means any gem with a color change controlled by crystal axis orientation. A = b c: hexagonal. A1 = a2 = a3 c. A b c: monoclinic. A b c: triclinic. Gems will normally be cut to show most attractive hues: tanzanite cut to minimize greenish-yellow hues, tourmaline, strong dichroism, zircon, ruby/sapphire, bow-tie effect , dichroic, cut with c-axis parallel to table. Oriented calcite crystal splits light coming through stone. Quick way to visually separate similar stone: garnet or spinel from ruby, garnet from tourmaline. Also used by cutters to orient stones prior to cutting. Different colors in different mixture of light wavelengths.
