Calcite (optical grade - old Mexico)

Item Description

A fine, large cleavage rhombohedron 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). Ex Dr. Vasco Trancoso Collection, a medical doctor and prominent mineral collector from near Lisbon, Portugal (https://www.mindat.org/user-11954.html). He assembled his mineral collection over the course of 60 years, and built a fine worldwide display collection that we recently purchased. Classic older material from Mexico.