Roger Weller, geology instructor
email@example.com copyright 2011-R.Weller
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.
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Just credit photo to R.Weller/Cochise College.