The below product (because of price, softness and how white it is) really sparks my interest in purchasing. Is it safe? http://www.amazon.com/School-Smart-Box-White-Sand/dp/B003U6QLVS/ref=lh_ni_t I have read that this can have odd-shaped grains and be pointy. Not sure how factual that is, though. Thanks in advance. Alex P.S. I'm not concerned with the softness or grain size. I just want to know if it's safe as far as ingredients and material wise.