Geol. 115 Study Guide for Lesson Four

What do you need to know (meaning understand, not just memorize) to do spectacularly well on Quiz 4? The essential terms and concepts are listed below. Writing out answers to each of the following would be an excellent way to prepare.

(Be able to define or recognize the definition of these terms and understand their useage in context). You can find the information in the web lesson -- on your test, do not expect exactly the same wording or examples as in your lesson. It would be a good idea to cross reference the defintions in the lesson with those you find in the texts.)

1) Essential Vocabulary

Luster, adamantine, vitreous, transparent, translucent, opaque, reflection, absorption, transmission, selective absorption, nanometer, chromophores, ions, idiochromatic, allochromatic, color zoning, hue, tone, saturation, cool colors, warm colors, "white diamond" fancy color diamond, beryllium diffusion, refractive index, dispersion aka "fire", optic character, DR (doubly refractive), SR (singly refractive), optic axis, birefringence (BR), pleochroism, dichroscope, dichroic, trichroic, non-polarized, plane polarized light, polariscope, "crossed filters", AGG reaction, relief, contact fluid, short wave UV, long wave, UV, fluorescence test, absorption spectrum, spectroscope.


2) Essential Concepts

From what do the optical properites of gems derive? Optical versus laboratory gemology, Difference between potential and actual luster of a gem, luster categories (adamantine, etc) and examples, degrees of transparency: examples, three fates of light hitting a gem, how related to transparency or lack of it, relationship between transparency and value, place of light in electromagnetic spectrum: relationship between wavelength and energy level, nanometer range of visible light, ROYGBiV, selective absorption and phenomenon of color, how do gems get their color?, how might chemical changes or radiation induce a change in color, allochromatic vs idiochromatic gems: examples, color from inclusions or patterns: examples, why are gems so carefully color graded?,gemological aspects of color: hue, tone and saturation: how is each described?, two hues in the GIA scheme that are not spectral colors, difference in saturation descriptions of "cool" and "warm" hues, system used to color grade diamonds: why no ABC?, relationship between color and value in diamonds, what is the actual technique used by diamond color graders?, differences between pre-modern gemology and that of today, behavior of light in relationship to gems: refraction, RI, what determines bending?, dispersion, what determines the potential and actual dispersion in a gem: effect of color and cut, examples of species with low and high dispersion., how dispersion affects the believability of diamond simulants: examples, optic character: SR, DR: which gems are which, how does the behavior of light differ in these two?, optic axis: definition and significance, birefrigence (BR) which gems have it, how measured, what is facet doubling?, pleochroism defintion and how measured: examples of pleochroic gems, consequences of strong pleochroism in a gem, optic character and light polarization, use of polariscope, SR, DR and AGG reactions to polariscope test: examples, refractive index, definiton, three ways to measure, degree of precision and limitations of each, significance of OTL reading, types of materials which can be tested on a refractometer, method for testing, fluorescence: definition, how tested? degree to which test is used, examples of useful fluorescent results, absorption spectrum, how measured, degree to which test is used.

3) Pronunciation Guide

(Clicking on the term will temporarily take you to a new web page to hear the pronunciation of the word. Depending on your browser configuration either put away the audio window, or use the back button to return to the list.)

adamantine, vitreous, diaphaneity, Prehnite, nanometer, chromophores, idiochromatic, allochromatic, Mookaite jasper, ametrine, Pezzottaite, Chelsea filter, padparashah, beryllium, refraction, YAG, strontium titanite, birefringence, pleochroism, dichroscope, Refractol, methylene iodide, petalite, phenakite, refractometer, fluorescence, almandite garnet