Silicon dioxide

Silicon dioxide, also called silica, is one silicon atom joined to two oxygen atoms. Oxygen and silicon are the two most common elements in Earth's crust, so their compound is everywhere: most sand is silica, and so are quartz, flint and opal.

In silica, each silicon atom sits at the center of four oxygen atoms, and each oxygen bridges two silicons. This builds a strong three-dimensional network. When the atoms line up neatly, you get crystalline quartz. When molten silica cools too fast for them to line up, it becomes glass. Nature made almost all of it, as molten rock cooled and as minerals dissolved and recrystallized. Industry mines sand and quartz, then washes, sorts, grinds or melts it, depending on the purity needed.

It's the main ingredient of every glass in a TV: Soda-lime glass, display glass and glass fiber. Ground into fine powder, it's the filler that makes up most of the weight of mold compound, the black plastic around chips. By way of quartz, it's also the raw source of silicon itself. Pure silica melts at about 1,700 °C, which is why other ingredients are added to make glass easier to work.