Faculty of Philosophy: The Amoral Sciences Club has a page about great beards of philosophy. Somebody better make a page for the great beards of science. Here are some initial suggestions.
The philosopher page claims Charles Darwin, but honestly he was more of a biologist than a philosopher.
Dmitri Mendeleev has always in my mind been the top contender for the real beard of science. Russian, flowing, elemental.

Ivan pavlov had a neatly conditioned beard.
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Louis Pasteur had a similar neat little beard. Not much space there for any microbiology.
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Wilhelm Röntgen on the other hand had a very opaque beard.
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Ludwig Boltzmann had a wilder beard that could only be described statistically.
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August Erlenmeyer of course had a conical beard.
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Antoine Becquerel had a radiant beard.
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James Clerk Maxwell on the other hand had a more wavy beard.

ibn al-Haytham (Alhazen), al-Khwarizimi and the other islamic golden age scientists (plus all the greek scientists) likely had impressive beards, but exact records do not seem to have survived.
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Conversely, if Aubrey de Grey gets SENS to work we will see his beard for a long time.