Is the World Really Running Out of Sand? — Practical Engineering
In fact, there are four specific kinds of sand, but they all fit this one criterion, and it's all about the size of the particles. At least half of those particles have to make it through a Number 4 sieve (about 5 millimeters), but no more than half can go through a Number 200 sieve (less than a tenth of a millimeter, or about 75 microns).
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