17007
Recent evidence suggests that the Vikings also made use of an optical compass as a navigation aid , using the light-splitting and polarisation-filtering properties of Iceland spar to find the location of the sun when it was not directly visible .
 Iceland
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Iceland