Sunstone is a type of feldspar, which when viewed from certain directions exhibits a spangled appearance. It has been found in Southern Norway, Sweden, various United States, including Oregon localities and on some beaches in South Australia. It is usually transparent to translucent. The optical effect, schiller, appears to be due to reflections from inclusions of red. These inclusions give the stone an appearance something like that of aventurine, hence sunstone is known also as "aventurine-feldspar". A theory exists that the sunstone had polarizing attributes and was used as a navigation instrument by seafarers in the Viking Age. A stone found in 2013 in the wreck of a 16th-century warship, may lend evidence of the existence of sunstones as navigational devices.
