Calcite Photos  
Cochise College               
Photos of Minerals
Geology Home Page

Roger Weller, geology instructor    copyright 2011-R.Weller

calcite-double refraction
One of the most outstanding optical properties displayed by the mineral calcite
is double refraction.  If a clear cleavage of calcite (often referred to as
"Iceland spar") is placed over a drawing of two crossed lines, inside the cleavage
it will appear that the lines have doubled.  Double refraction is a result of the
calcite being optically anisotropic.  In simpler terms, light passing through the
calcite cleavage travels at different speeds depending upon the direction through
the crystalline structure.  A light ray entering calcite is split into two separate rays,
each traveling a slightly different path to create two separated images. 
This optical property is also known as birefringence.


calcite                                                                                                                             icelandspar
Photo is copyright free for non-commercial educational uses.
Just credit photo to R.Weller/Cochise College.