sunstone

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sunstone.

1 Crystal mineral thought by some to have been used by the Vikings as an aid to navigation, especially in conditions of low visibility due to clouds or fog when the position of the sun was uncertain. Both Iceland sparIceland spar,
colorless variety of crystallized calcite, characterized by its properties of transparency and double refraction. It is used chiefly in the manufacture of Nicol prisms, which are essential parts of polarizing microscopes and other optical instruments.
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 and cordierite, which have optical properties that cause rays of light to show different properties in different directions, thus permitting an observer to determine the position of the sun, have been suggested as candidates for the sunstone. 2 A reddish or golden form of a plagioclase feldsparfeldspar
or felspar
, an abundant group of rock-forming minerals which constitute 60% of the earth's crust. Chemically the feldspars are silicates of aluminum, containing sodium, potassium, iron, calcium, or barium or combinations of these elements.
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 that is used as a gemstone.

sunstone

[′sən ‚stōn]
(mineralogy)
An aventurine feldspar containing minute flakes of hematite; usually brilliant and translucent, it emits reddish or golden billowy reflection. Also known as heliolite.
References in periodicals archive ?
Sunstone Circuits earned this award for the fourth year in a row, by maintaining a formal wellness program to encourage healthy lifestyles.
In 2011, a research team led by a French physicist named Guy (http://rspa.royalsocietypublishing.org/content/early/2011/10/28/rspa.2011.0369) Ropars built a sunstone using a bit of Iceland spar set into a wooden case that directed light from the sky onto the crystal.
Despite the literary references, no intact sunstone has been found on Viking sites.
"It's unprocessed, so you have a good chance of finding sunstones," Schenk said.
But the odds of finding lots of high-quality sunstones improve by sifting through the highest-grade ore, selected for commercial processing.
Visitors can get access to that ore for a fee, and many serious rockhounds are willing to pay for the opportunity to collect more sunstones in less time.
- a white-bearded gent who looks like a prospector right out of Central Casting - paid $200 for the right to pick sunstones off the mine's commercial screening plant conveyor belt for one hour.
The Knoxes collected three to four pounds of sunstones in their hour, during which the plant's mechanized screens sifted likely material from about six tons of dirt and larger rock.
Sprayed with water as they moved along the belt, the sunstones sparkled, making them easy to spot among similar-sized rocks.
"We definitely got some nice sunstones - nice size and some with nice color," Cynthia Knox said.
Reed and Debra Grote of Redmond, however, preferred to prospect for sunstones the old-fashioned way.
The sunstone proposal just outlined presumes that the Vikings observed the sky's polarization to find the direction north (if they knew the time of day).