dichroscope
/ˈdʌɪkrəskəʊp/(also dichroiscope)
noun
Any of several instruments, typically hand-held, for observing or examining the dichroism of crystals and gemstones, often with a view to identification.
Origin
Mid 19th century; earliest use found in David Brewster (1781–1868), natural philosopher and academic administrator. From ancient Greek δίχρους two-coloured + -scope, after dichroism.