What are the small crystals resembling glass that are occasionally found in canned seafood?

These harmless crystals, called struvite, are formed by magnesium, ammonia and phosphate, elements occurring naturally in seafood. Sometimes, during the cooking process, these elements crystallize to form what looks like tiny particles of glass. They are safe if consumed, as natural stomach acids will dissolve the crystals, which are then absorbed by the body. They also dissolve when boiled in lemon juice or vinegar.