My favorite non-glass vintage marbles, agates, required much skill and labor to produce. Their high price reflected this. Many kids could not afford to own one. Early machine made marble producers would later try to mimic these agates of yore, in more fragile but affordable glass.
Unlike their contemporary handmade clay commies or glassies, agates were perfectly round, extremely hard, and heavy. That made them deadly accurate shooters. Shot by a pro, agates could split lesser marbles in half and then "stick" in the dirt with hardly a roll. Such marbles could withstand years, even generations, of rugged marble game combat.
I recently stumbled upon a terrific article from the June 3, 1882 edition of Scientific American, entitled Where Agates Come From. It will give you some appreciation for what went into these magnificent marbles.