calcite - cleaved rhombs of Iceland spar - transparent calcite that shows double refraction - Unit of 5 student specimens

$ 7.70

Calcite: CaCO3    -  Calcite is an extremely common rock forming mineral. In pegmatites it forms large masses and it makes up some limestones almost entirely. It has a large variety of crystal forms, but these do not include the rhombus-shaped pieces that are sold as “calcite crystals.” The rhombs are produced by cleaving calcite in three directions between rows of atoms. 

Optically clear calcite that is free of impurities exhibits strong double refraction. When a calcite rhomb is placed above a line drawn on paper and rotated, the drawn line doubles or becomes single depending on the angle of rotation.

This calcite was mined in Morocco and cleaved into rhombs in Italy. The preparation was particularly good. For an interesting and more detailed explanation of double refraction in calcite, and of its use in Viking navigation, see this article.


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