We are probably not talking about the same ones. Here from the one I got:
Carbonato de Calcio (CaCO3): 27,70% ± 0,2%
Óxido de silicio (SiO2): 70,30% ± 2%
Alúmina (Al2O3): 1,11%
Óxido de magnesio (MgO): 0,42%
Trazas entorno al 0,5%
This was actually recommended from 2 good growers that don't...