/usr/share/mimelnk/chemical/x-mdl-rdfile.desktop is in chemical-mime-data 0.1.94-6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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Encoding=UTF-8
Type=MimeType
MimeType=chemical/x-mdl-rdfile
Comment=MDL Reaction Format
Comment[de]=MDL Reaktions-Format
Comment[fr]=Format MDL de Réactions
Icon=chemistry
Patterns=*.rd;
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