'Microscopic identification of crystals' -- subject(s): Chemical
microscopy, Crystal optics
'Crystal identification with the polarizing microscope' --
subject(s): Crystal optics
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positive crystal (pluralpositive crystals)
(optics) a doubly refracting crystal in which the index of refraction for the extraordinary ray is greater than for the ordinary ray, and the former is refracted nearer to the axis than the latter, such as as quartz and ice
negative crystal (pluralnegative crystals)
(optics) A uniaxial crystal, such as one of calcite, in which the extraordinary wave travels faster than the ordinary wave