Silica is a mineral commonly found in nature as quartz. It is inorganic and is hardly absorbed in the body. However, the plant horsetail (Equisetum arvense) is a rich source of organically bound silicon, which the body can easily absorb. Silica is normally found in our bones, teeth, connective tissue, blood vessels, skin, hair, and nails. In fact, we have it in all our cells in different concentrations.