glass is made from sand,
there is less glass in world then sand,
and again,
why lock more precious commodity in another product
which we are already making from other less precious commodity ?
It's the shape of the grains of sand that's bad for concrete, not the chemical composition. It gets less angular and more round when it moves in the desert and it doesn't bound well with cement. Sand that is good for concrete is rare and making it is expensive. The "bad" sand that is common everywhere is still perfect to make glass.
