alt Hacker NewsSodium-ammonium tartrate (I remembered what you were talking about, but had to look up the actual chemical!)
https://pmc.ncbi.nlm.nih.gov/articles/PMC9291139/
From that:
"To his surprise, he noticed that each crystal has a tiny facet on one of its edges oriented sometimes to the right and sometimes to the left. He could separate them by hand with a tweezer."
It's moments like that, and Kekule's story of the snake dream for benzene that make me feel unworthy of being a scientist. I sometimes wonder: in my career of looking at things, did I miss something fundamental and significant simply because my powers of observation and general intelligence were insufficient?