Clay minerals are not much to look at, but life on Earth depends on them.

At the microscopic level, clays are tiny flakes, like mica but infinitely smaller. At the molecular level, clay is a sandwich made of sheets of silica (SiO4) tetrahedra and sheets of magnesium or aluminum hydroxide  and Al . Some clays are a proper three-layer sandwich too

What makes clays so valuable for life is that with their tiny particle size and open-faced construction, they have very large surface areas and can readily accept many substitute cations for their Si, Al and Mg atoms. Oxygen and hydrogen are available in abundance. From the viewpoint of microbes, clay minerals are like machine shops full of tools and power hookups. Indeed, even the building blocks of life amino acids and other organic molecules are enlivened by the energetic, catalytic environment of clays.