Sunstone (500 gram bag) from Tanzania "made in Germany" with a 50% discount!

The mineral oligoclase or sunstone is a sodium calcium aluminum tectosilicate with the chemical formula (Na, Ca) (Si, Al) 4O8. It belongs to the feldspars. The colorless, greenish, gray or brown oligoclase has a glass luster, a white stripe color, a perfect cleavage according to crystal plane [001] and a good according to [010]. The average density is 2.65 and the hardness is 7. The crystal system is triklin and the mineral is neither radioactive nor magnetic. The name of the mineral oligoclaas is derived from the Greek words oligos and klasein, "little splitting". Oligoclaas is a very common feldspar in metamorphic and igneous rocks such as pegmatite. It is part of the plagioclase series (albite-anorthite). The type location of oligoklaas is Twedestrand in Norway. Presumably, the Vikings used oligoclaas as a navigation tool to determine the position of the sun at sea in cloudy weather. This mineral can reveal polarized light that forms circles around the sun due to refraction in the atmosphere. The crystal doubles the rings. If both are equally visible, the crystal is pointed directly at the sun. The rings are also visible when the sun has already set.