Iceland spar shows off calcite's birefractiveness very well. Iceland spar is used in the optics industry for it's transparency and ability to split images.
Calcite (sparry) (Iceland Spar)CaCO3
Class: Carbonate
Hardness: 3
Density: 2.7
Streak: White
Lustre: Vitreous
Habit: Large crystals, some exhibiting common twin striae
Colours: White ...
A form of calcite, Iceland spar, plays a critical role in the plot of Against the Day by Thomas Pynchon. The same form is referred to in The Amber Spyglass by Philip Pullman as it has very similar properties to a mineral found in that story.
aka Calcspar, Cave Onyx, Flowstone, Iceland Spar, Lime Spar, Mexican Jade, Mexican Onyx, Nailhead Spar, Pineapple Jasper
Calcite is the one of the most common minerals on earth, constituting about 4% of the Earth's crust by weight.
"Iceland spar" is a colorless form of calcite found in Iceland. It forms fascinating crystals. If you put a piece of Iceland spar over print and look through it the print will appear doubled.
Chemical composition -- Calcium carbonate. The colorless transparent crystals are known as Iceland spar.
Color -- Colorless or shades of pink, purplish red (cobaltocalcite), green, blue, yellow.
What has happened is that the light passing through the square hole (C of Fig. 3) has divided in passing through the strongly doubly refracting Iceland spar (B of Fig. 3) and two images of the square hole are thus produced.
calcite - is a very soft mineral that occurs in a transparent to semitranslucent material, in a wide variety of color and patterns. Some of the varieties include Iceland spar, satin spar, marble and travertine. Sources: widespread.
It is thought that the Vikings actually used the light-polarizing properties of a stone to tell the direction of the sun on cloudy days. While this “sun stone' is thought to have actually been Iceland spar (calcite) or iolite, ...
hitting a gemstone splits into two rays traveling through the stone at different speeds and in different directions, the reaction is called birefringence or double refraction. This is seen uncommonly and in a variety of calcite called Iceland Spar as ...
The Norse Vikings revered a mineral which they called "sunstone" that was actually a transparent variety of calcite called "Iceland spar" that is totally unrelated to the aventurine feldspar variety of sunstone.
Double refraction is the breaking up of a ray of light into two rays, the ordinary ray and the extraordinary ray, when it passes through some materials like calcite also called Iceland spar.
However, in some minerals, such as the Iceland Spar variety of Calcite it is strongly seen. The double refraction is different in every mineral, and thus can be used to identify gems.
 See also: Calcite, Crystal, Color, Transparent, Stone
|
