<?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">allotropes</topic></authority><related type="broader"><topic>materials by chemical form</topic></related><variant type="other"><topic>allotrope</topic></variant> <note xml:lang="en"><![CDATA[ Structurally distinct forms in which a chemical element may occur. Some chemical elements may exist in two or more different forms, in the same physical state. Allotropes are different structural modifications of an element; the atoms of the element are bonded together in a different manner. ]]></note></mads>