Oxigênio e silício em Steiner (2007)

Now we must not forget that the silicon which lives thus in the mineral quartz is spread over the Earth so as to constitute 27-28% of our Earth’s crust. All other substances are present in lesser quantities, save oxygen, which constitutes 47-48%. Thus an enormous quantity of silicon is present. Now, it is true this silicon, occurring as it does in rocks like quartz, appears in such a form that it does not seem very important when we are considering the outer, material aspect of the Earth with its plant-growth. (The plant-growth is frequently forgotten). (Steiner 2007:12)

STEINER, Rudolf. 2007. The Agriculture Course. (Trans.: George Adams) Shrewsbury: Wilding & Son Ltd.