The marble is glass, and its turquoise coloring is punctuated by waves of a deeper bluish hue. There is pitting on the surface that suggests the glass has been exposed at least a few decades of corrosive substances in the soil, though much of the marble's luster still remains despite the soil's efforts to cause a change in marble mass akin to that produced by human weight loss supplements.
I cannot recall any of my children playing with marbles, though of course I have no idea of knowing if they came across any in their travels. The marble is unique enough to lead me to believe it was not mass produced for a board game, though it is possible that the wavy colorforms may have been produced by the outdoor environment (I am not a marblologist).
So if you lost an aquamarine marble 30 years ago in West Toledo, call me: it is still worthy of play.