This is intended as a list of, or links to, stone currently or historically produced in various countries (not generic types of stone).
See also:
Greece
Italy
United Kingdom
Limestone
Also see:
... our quadratic equation by a, we have <math> x^2 + \left( \frac{b}{a} \right) x + \frac{c}{a}=0 </math> which is equivalen ...