Natural Big Yellow Optical Calcite Iceland Spar 155g

Photographed from a single angle, this optical calcite rhomb shows a warm honey-gold body color that deepens to amber tones near the base. The classic slanted rhombohedral cleavage form is clean and well-defined, with fine ghost-like growth lines tracing across the broad face. The material has a glassy, translucent quality that lets light travel well into the thinner sections, giving the crystal a soft inner glow.

Optical calcite, also called Iceland spar, is calcium carbonate crystallized into large, flawless cleavage blocks. It earns the name 'optical' from its strong birefringence (double refraction): light entering the crystal splits into two separate rays, so that any line or pattern viewed through a clear section appears doubled. Historically, calcite from Iceland was the material used to first study this effect scientifically, and it later found practical use in polarizing microscopes before synthetic materials took over. This piece is sourced from China, one of the main commercial sources of optical calcite today. Untreated and natural, it makes a satisfying desk or shelf specimen, and a good piece for demonstrating the double-refraction effect firsthand.

Natural yellow optical calcite (Iceland spar), China - sold as a single piece.