Iceland spar
Encyclopedia
Iceland spar, formerly known as Iceland crystal, is a transparent variety of calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

, or crystallized calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...

, originally brought from Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...

, and used in demonstrating the polarization of light (see polarimetry
Polarimetry
Polarimetry is the measurement and interpretation of the polarization of transverse waves, most notably electromagnetic waves, such as radio or light waves...

). It occurs in large readily cleavable
Cleavage (crystal)
Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the...

 crystals, easily divisible into rhombs, and is remarkable for its double refraction. Historically, the phenomena of this crystal were studied at length by Christiaan Huygens and Isaac Newton
Isaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...

. Sir George Stokes also studied the phenomenon.

Mine
Mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...

s producing Iceland spar include many mines producing related calcite and aragonite
Aragonite
Aragonite is a carbonate mineral, one of the two common, naturally occurring, crystal forms of calcium carbonate, CaCO3...

 as well as famously in Iceland, productively in the greater Sonoran desert
Sonoran Desert
The Sonoran Desert is a North American desert which straddles part of the United States-Mexico border and covers large parts of the U.S. states of Arizona and California and the northwest Mexican states of Sonora, Baja California, and Baja California Sur. It is one of the largest and hottest...

 region as in Santa Eulalia, Chihuahua
Santa Eulalia, Chihuahua
Santa Eulalia is a town and seat of the municipality of Aquiles Serdán, in the northern Mexican state of Chihuahua. As of 2005, the town had a total population of 2,089.Founded in 1652 by Diego del Castillo, it is one of the oldest settlements in the state....

, Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

 and New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...

, United States, as well as in the People's Republic of China
People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...

.

Viking "sunstone"

It has been speculated that the sunstone
Sunstone (medieval)
The sunstone is a type of mineral attested in several 13th–14th century written sources in Iceland, one of which describes its use to locate the sun in a completely overcast sky. Sunstones are also mentioned in the inventories of several churches and one monastery in 14th–15th century Iceland...

 (a different mineral than the gem-quality sunstone
Sunstone
Sunstone is a plagioclase feldspar, which when viewed from certain directions exhibits a brilliant spangled appearance; this has led to its use as a gemstone. It has been found in Southern Norway, and in some United States localities...

) mentioned in medieval Icelandic texts was Iceland spar and that Viking
Viking
The term Viking is customarily used to refer to the Norse explorers, warriors, merchants, and pirates who raided, traded, explored and settled in wide areas of Europe, Asia and the North Atlantic islands from the late 8th to the mid-11th century.These Norsemen used their famed longships to...

s used its light-polarizing property to tell the direction of the sun on cloudy days, for navigational purposes.

In 2007, Ramón Hegedüs and his colleagues from Eotvos Lorand University in Budapest
Budapest
Budapest is the capital of Hungary. As the largest city of Hungary, it is the country's principal political, cultural, commercial, industrial, and transportation centre. In 2011, Budapest had 1,733,685 inhabitants, down from its 1989 peak of 2,113,645 due to suburbanization. The Budapest Commuter...

, Hungary
Hungary
Hungary , officially the Republic of Hungary , is a landlocked country in Central Europe. It is situated in the Carpathian Basin and is bordered by Slovakia to the north, Ukraine and Romania to the east, Serbia and Croatia to the south, Slovenia to the southwest and Austria to the west. The...

, confirmed that the polarization of sunlight in the Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...

 can be detected under cloudy conditions. Their research is reported in "The Proceedings of the Royal Society
Proceedings of the Royal Society
Proceedings of the Royal Society is the parent title of two scientific journals published by the Royal Society, whereas its initial journal, Philosophical Transactions, is now devoted to special thematic issues...

." Further research reported in the Royal Society, 2011, also confirms this was easily achieved, even in cloudy twilight conditions, using nothing more than a sunstone and the naked eye http://rspa.royalsocietypublishing.org/content/early/2011/10/28/rspa.2011.0369.

In literature

Thomas Pynchon
Thomas Pynchon
Thomas Ruggles Pynchon, Jr. is an American novelist. For his most praised novel, Gravity's Rainbow, Pynchon received the National Book Award, and is regularly cited as a contender for the Nobel Prize in Literature...

 refers to the doubling property of Iceland spar in his 2006 novel Against the Day
Against the Day
Against the Day is a novel by Thomas Pynchon. The narrative takes place between the 1893 Chicago World's Fair and the time immediately following World War I and features more than a hundred characters spread across the United States, Europe, Mexico, Central Asia, and "one or two places not strictly...

. A section of the novel is entitled "Iceland Spar".

Phillip Pullman refers to the doubling property of Iceland spar in his 2000 novel The Amber Spyglass
The Amber Spyglass
The Amber Spyglass is the third and final novel in the His Dark Materials series, written by English author Philip Pullman, and published in 2000....

, the third volume in the His Dark Materials
His Dark Materials
His Dark Materials is a trilogy of fantasy novels by Philip Pullman comprising Northern Lights , The Subtle Knife , and The Amber Spyglass...

trilogy.

External links

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