<?xml version="1.0" encoding="utf-8"?><mads xmlns="http://www.loc.gov/mads/" xmlns:mods="http://www.loc.gov/mods/v3" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.loc.gov/mads/
mads.xsd"><authority><topic authority="http://AATesaurus.cultura.gencat.cat/aat/getty_en">Iceland spar</topic></authority><related type="broader"><topic>calcite</topic></related><variant type="other"><topic>Icelandic spar</topic></variant><variant type="other"><topic>spar, Iceland</topic></variant> <note xml:lang="en"><![CDATA[ Transparent, naturally-occurring calcite crystal used in demonstrating the polarization of light.  An oblong stone made of Iceland spar found in the wreck of a 16th-century English warship in 2013 has led archaeologists to speculate that the crystal is one and the same as the sunstone, a near-mythical navigational aid said to have been used by Viking mariners. ]]></note></mads>