Iceland spar Calcite (optical grade - old Mexico) Kidwell Coll.

Item Description

An impressive large old cleavage rhomb of water-clear optical grade Iceland spar calcite from an unknown locale in Chihuahua State, Mexico. The rhomb has classic calcite birefringence. Birefringence is formally defined as the double refraction of light in a transparent, molecularly ordered material, which is manifested by the existence of orientation-dependent differences in refractive index (https://www.microscopyu.com/techniques/polarized-light/principles-of-birefringence). The rainbow optical effects add character. Ex Al Kidwell Collection and acquired in 1966. Al was a well-known mineral collector and research geologist for Exxon. He passed away in 2008. The Phosphate Kidwellite is named for him. A very fine old example of optical grade calcite from the locale - the textbook example you LITERALLY would have seen in gradeschool textbooks!