The mineral oligoclave or sunstone is a sodium calcium aluminum tectosilicate of the chemical formula (Na, Ca) (Si, Al) 4O8. It belongs to the field spots. The colorless, greenish, gray or brown oligoclase has a glass gloss, a white dash, a perfect splitting according to crystal plane  and a good according to . The average density is 2.65 and the hardness is 7. The crystal system is trichlien and the mineral is neither radioactive nor magnetic. The name of the mineral oligoclasa is derived from the Greek words oligos and klasein, "little splits". Oligoclast is a common field splash in metamorphic and coagulation rocks as pegmatite. It is part of the plagioclaas series (albiet anorthite). The type location of oligoclaas is Twedestrand in Norway. Presumably, the Vikings used oligoclaas as a navigation tool to determine the position of the sun at cloudy weather. This mineral can reveal polarized light that forms circles around the sun due to the refraction in the atmosphere. The crystal doubles the rings. If both are equally visible, the crystal is directed to the sun. The rings are also visible when the sun is already underneath.