Calcite Iceland Spar /Optical Calcite - Spirit Rock Shop
Iceland spar - Wikipedia
Optical Calcite Raw Viking Sunstone Iceland Spar Pendant - Etsy
Viking Sunstone (Optical Calcite) | prettygoods
Icelandic spar, also known as optical calcite, Icelandic crystal, and Viking sunstone. Vikings would use its light-polarizing properties to locate the sun to navigate the seas even on the cloudiest of days. :