cheese crystals

What is up with them? Sometimes when I buy a kinda aged/hard cheese (like those mediocre "Irish" cheese in the fancy cheese section at the big grocery store, where the cheese is always expired), it has very small crunchy crystals in it. First I thought it might have been a symptom of going bad. But unless a food is obviously rotten to the core, I usually either salvage the good parts or, if I'm not sure, eat it anyway. I don't think this approach has ever failed me. Anyway, I really wonder what those crystals are and what causes them. Precipitated salt when the cheese has been sitting around for a while after the aging process? I dunno. Halp please.