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level: Uses of light in gemmology

Questions and Answers List

level questions: Uses of light in gemmology

Question	Answer
What is the term used to describe the return by the surface of a gemstone of some or all of the light that falls on it?	Reflection
What is the name for light that reaches the surface of a gemstone?	Incident
What is the term used to describe the angle at which light is reflected from the surface of a gemstone?	Angle of Reflection
What is the name of the imaginary line that the incident ray and the angle of reflection are measured against?	Normal
What is the name of the effect that causes light rays to bend towards the normal as they enter a gemstone?	Refraction
What is the property of a gemstone that tells us the speed of light between the angle of incidence and angle of refraction of a particular stone?	Refractive Index
What is the refractive index a measure of in terms of population of electrons slowing down light within a certain type of gem?	Optical Density
What is the name of the effect that enables you to find out the Refractive Index of a gemstone?	Total internal reflection
What is the name of the effect caused when light entering a gemstone is split into two separate rays?	Double refraction
What is the term used to describe light passing through an amorphous material, causing it to behave in exactly the same way regardless of the direction it travels in?	Isotropic
What two types of materials always have a single refractive index?	Cubic
What is the term for gemstone materials that possess directional properties?	Anisotropic
What six crystal systems are optically anisotropic?	Tetragonal
What is the name for a ray of light that has waves of light vibrating in all different directions, with no order?	Non-Polarized
What is the name for a ray of light that has passed through a polarizing filter, causing the light waves to vibrate in the same, orderly direction?	Polarized
What type of gem material produces plane polarized light?	Anisotropic
What is the term used to describe the difference between the two separate RI readings seen in anisotropic gem materials?	Birefringence
What is the name of the optical effect seen in gemstones that exhibit double refraction?	Doubling
What is the name for anisotropic gemstones that only have one optic axis?	Optically Uniaxial
What is the name for anisotropic gemstones that have two optic axes?	Optically Biaxial
What is the term used when the angle of incidence is at 90 degrees to the normal, causing it to pass along the surface of the gemstone?	Critical Angle
What is the term given to the optical effect where the angle of refracted light is more than 90 degrees from the normal, causing it to be reflected back inside the gemstone?	Total Internal Reflection