This is the first convincing "candidate" I've seen for dark matter, which I've been ready to dismiss as cosmological fiction for just that reason. As well as being totally stable, sexaquarks would apparently not interact with ordinary matter -- or each other. There would be something in the six-quark arrangement that would cancel out the strong force and they would (presumably) be electrically neutral as well, all of which would explain the non-interaction, so they might form clouds but never really congeal into physical bodies of any kind....