“Cannabinoid acids can crystallize, but many cannabinoids, including THC, cannot. CBD is one exception because it has 2 OH groups that can interact (hydrogen bond) with OH groups on other CBD molecules. THC, on the other hand, only has one OH group, so it can only hydrogen bond to one other THC, making a dimer. The carboxylic acid group on THCa acts as a 2nd functional site on the molecule, allowing crystal lattices to grow, similar to the way CBD’s 2 OH groups allow crystal growth.” - someone on this forum, probably @Photon_noir