Definition

Noun: A clear, colorless variety of the mineral calcite (calcium carbonate). It is characterized by its strong double refraction property, meaning it splits a single light ray into two separate rays. Historically significant, it is named for its original discovery location.

Usage

This term is used specifically in geological, optical, and scientific contexts to refer to this particular type of calcite crystal. * Early navigators used pieces of Iceland spar as a primitive sunstone to locate the sun on cloudy days. * The optical clarity of Iceland spar makes it valuable for demonstrating the polarization of light. * The specimen of Iceland spar on display shows perfect cleavage rhombohedrons.

Advanced Usage

• In Polarization: is famously used in Nicol prisms, an optical device invented by William Nicol in 1828. A Nicol prism is constructed by cementing two precisely cut pieces of together with Canada balsam. This device is used to produce a beam of polarized light, which is essential in polarizing microscopes and other optical instruments for studying the properties of minerals and materials.

Variants and Related Words

• Calcite (n): The common mineral form of calcium carbonate (CaCO₃), of which Iceland spar is a transparent, optically pure variety.
• Calcium Carbonate (n): The chemical compound (CaCO₃) that forms calcite, limestone, chalk, and marble.
• Double Refraction (n): Also called birefringence. The optical property, exhibited strongly by Iceland spar, where a single incident light ray is split into two rays traveling at different speeds.
• Polarizing Microscope (n): A microscope that uses polarized light, often generated with prisms made from materials like Iceland spar, to examine the optical properties of specimens.

Synonyms

• Transparent calcite
• Optical calcite

Related Phrases / Terms

• Nicol prism: An optical device made from Iceland spar for producing polarized light.
• Sunstone: A historical term sometimes used for Iceland spar due to its alleged use in Viking navigation.
• Birefringent crystal: A general term for any crystal, like Iceland spar, that exhibits double refraction.

Noun

1. a transparent calcite found in Iceland and used in polarizing microscopes