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

Item Description

A striking large cleavage rhomb of optical grade Iceland spar calcite from an unnamed Coahuila locale near Melchor Muzquiz, famous for fluorite and celestine. 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 Bill Panczner Collection : Bill was the first Curator of Earth Science at the Arizona Sonora Desert Museum in 1974 and the author of the 1987 book Minerals of Mexico. It is the most thorough summary of the subject. Read about Bill in the Mineralogical Record Biographical Archive at: https://mineralogicalrecord.com/labels.asp?colid=841. A fine example of optical grade calcite from the obscure locale - the textbook example you LITERALLY would have seen in gradeschool textbooks!