<?xml version="1.0" encoding="utf-8"?><!DOCTYPE Zthes SYSTEM "http://zthes.z3950.org/xml/zthes-05.dtd">  <Zthes><term><termId>31375319</termId><termName>Iceland spar</termName><termType>PT</termType><termNote><![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. ]]></termNote><termCreatedDate>2026-03-30 20:41:13</termCreatedDate><relation><relationType>UF</relationType><termId>31375320</termId><termName>Icelandic spar</termName><termType>ND</termType></relation><relation><relationType>UF</relationType><termId>31375321</termId><termName>spar, Iceland</termName><termType>ND</termType></relation><relation><relationType>BT</relationType><termId>31344461</termId><termName>calcite</termName><termType>PT</termType></relation></term>  </Zthes>