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level: Tools in depth - The polariscope

Questions and Answers List

level questions: Tools in depth - The polariscope

Question	Answer
In a polariscope or polarizing microscope, what is the name for the upper and lower polarizing filters?	Polarizer and analyser
When testing gemstones for anisotropy, what position must the two filters be set in when using the polariscope?	Crossed
If a gem material remains dark when placed between the crossed polarizing filters and rotated, due to the plain polarized light passing through the stone and being absorbed by the analysing filter, what sort of gem material is it?	Isotropic
If a gem material goes light and dark with every 90 degree rotation between polarizing filters when the gems vibration directions line up with the polarizing filter as the plane polarized light passes through, what type of gem material is it?	Anisotropic
If a stone remains light during a complete rotation between polarizing filters, due to none of the crystal materials that make up the gem being parallel to eachother, what type of gem material is it?	Polycrystalline
What features of a gem material can cause a false reading when using a polariscope?	Inclusions and cleavage cracks
What is the name of the sperical glass rod used to view interference figures in gemstones alongside a polariscope?	Conoscope rod
What is the name for the patterns of light and dark that reveal the directions of the optic axes, and reveal whether a stone is uniaxial or biaxial, when viewed using a conoscope rod?	Interference figures
What should you look for in a faceted gemstone under a polariscope in order to try and ascertain the inteference figure?	Irridesence
What types of gem materials do you not necessarily need a conoscope to view the inteference figure?	Cabochons and beads
How many optic axes are shown in this inteference figure as seen through a concoscope rod?	Two
How many optic axes are visible in this inteference figure, seen through the conoscope rod?	One
What type of gem material would this inteference figure be seen in?	Uniaxial
What type of gem would this distinctive "bulls-eye" inteference figure be seen in?	Quartz