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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.
..... Click the link for more information. 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
, 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.
..... Click the link for more information. that is used as a gemstone.
An aventurine feldspar containing minute flakes of hematite; usually brilliant and translucent, it emits reddish or golden billowy reflection. Also known as heliolite.