Islamic spar ( eng. Iceland spar, silfurberg isl ) is a transparent crystalline type of calcite ( calcium carbonate - CaCO 3 ). It was named after the location of the discovery of the first large Eskifjordur field near the city of Helgastadir in Iceland [1] .
| Iceland spar | |
|---|---|
 Iceland Spar Crystal | |
| Formula | CaCO3 |
| Physical properties | |
| Colour | transparent |
| Density | 2,711 g / cm³ |
| Syngony | |
Content
Properties
Historically, this name has been used in mineralogy since the end of the 17th century, when crystals of this transparent mineral were brought from Iceland. When viewed through a transparent crystal of Iceland spar a double image is seen. The crystallographic form of crystals of Iceland spar most often has the form of a scalenehedron [1] .
The crystals have a different color, mostly pale: blue, pink, yellow, colorless or a different shade. Coloring depends on impurities of manganese, iron, magnesium, rarely barium, lead, strontium and bitumen.
Use
Due to the high birefringence of light (0.172) and good transparency in the visible and ultraviolet spectral range, it is used in optical and optoelectronic systems for polarizing light and controlling light fluxes, for example, in the polarizing Nicol prism . Single crystals without cracks and containing a small number of foreign inclusions are used. There are two groups of raw materials: A - for work in a wide light range; B - only in red and infrared light [1] .
In 1669, Danish scientist Rasmus Bartolin discovered the double refraction property of a light beam by Iceland spar and published an exact description of the phenomenon. In 1690, the Dutch physicist Christian Huygens described the optical properties of Iceland spar as it is presented in modern physics textbooks. But probably the Vikings used the properties of the mineral in practice long before these discoveries. There is an opinion that it is the Icelandic spar that is the legendary “sun stone” of the Vikings , with the help of which they were guided by the sun in cloudy weather [2] . When observing cloudy areas of the sky and rotating the crystal, one can detect areas in the sky, from which, as a result of Rayleigh scattering , fully polarized light emanates. Perpendiculars to the line connecting such areas indicate the position of the hidden sun in the clouds [3] .
In 2003, a crystal of Iceland spar, along with remnants of other navigational instruments, was found among the wreckage of an English vessel that sank in the English Channel in 1592 . Although the main journeys of the Vikings were made in the 9th — 10th centuries, it is believed that spar crystals could be used for navigation and later as an alternative to the magnetic compass brought to Europe from China in the 13th century. [3] [4]
Prey
A large deposit of Iceland spar is located near the town of Helgastadir near Esquifjordura in Iceland, where optical quality crystals were mined from cavities in basalt . Also known are deposits in South Africa , Mexico , Evenkia , Yakutia , Tuva , Central Asia and the Caucasus [1] .
Notes
- ↑ 1 2 3 4 Iceland Spar // Mountain Encyclopedia / Ch. Editor E. A. Kozlovsky. - M .: Soviet Encyclopedia, 1986. - T. 2. - p. 460.
- ↑ The secret of "sunstones": how did the Vikings get from Norway to Greenland almost blindly
- ↑ 1 2 BBC: “The Viking sun stone was found on an old ship”
- Through the magic crystal. Viking mythical compass turned out to be a reality
Literature
- Skropyshev A.V., Kukui A.L. Iceland spar. L: 1973
- Kievlenko E. Ya. Geology and field assessment of Iceland spar M: 1974
Links
- Iceland Spar // Brockhaus and Efron Encyclopedic Dictionary : 86 tons (82 tons and 4 extra). - SPb. , 1890-1907.
- Iceland spar on the "Catalog of Minerals" Photos, description, deposits (rus.) .