gentoo-overlay/app-misc/xmind/files/x-xmind.xml

<?xml version="1.0" encoding="UTF-8"?>
<mime-info xmlns="http://www.freedesktop.org/standards/shared-mime-info">
   <mime-type type="application/x-xmind">
     <sub-class-of type="application/zip"/>
     <comment>XMind Workbook</comment>
     <alias type="application/vnd.xmind.workbook"/>
     <generic-icon name="package-x-generic"/>
     <glob pattern="*.xmind"/>
   </mime-type>
</mime-info>