[johnco]

"they made great ammo for the slingshot"
especially after boiled, cooled in cold water so they would fracture. we called it cracking them. exploding ammo that shattered on contact. our "special" cateye marbles, only available thru us, were traded 1 for 2 crystals or 5 cateyes on the 4th grade playground blackmarket. the rare " special" crystals were worth much more. we kept the good ones from the trade and transformed the less valuable cateyes that afternoon. since everyone's "collector" marbles fell apart with the slightest contact, they would line up to trade for more the next day. had a good little racket going for a while.we had boxes of crystals in clear, blue, green and black we then traded for other stuff. and so began a lifetime of wheeling and dealing.