How well do you know the periodic table? Our series The Elements explores the fundamental building blocks of the observable universe—and their relevance to your life—one by one.

Silicon is a metalloid: an element with properties not quite like a metal, nor exactly like a non-metal. If you have a cell phone in your pocket or dirt on your shoes, you’re carrying silicon. Learn more about this ever-present element.

1. IT'S JUST ABOUT EVERYWHERE.

It's the seventh most abundant element in the universe and even more prevalent in the Earth's crust, second only to oxygen as the most common element by weight. The layer under the crust—the mantle—is rich in silicon as well. With an atomic number of 14, it sits right below carbon on the periodic table.

2. SILICON ISN'T THE SAME THING AS SILICONE.

iStock

The word silicone might make you think of breast implants, but it's actually a general term for a group of synthetic substances made of alternating silicon and oxygen atoms, with carbon and hydrogen molecules bonded on the sides. By mixing up these side groups of molecules and creating links between chains, chemists can create silicones with all sorts of different properties. Yes, you can find silicones in breast implants, but also in car polish, the insulation around electric cables, and even in your hair conditioner, where they help to calm down frizz. We can also thank silicones for Silly Putty, which was invented during World War II, when scientists were trying to create an alternative to rubber—and instead came up with a new national favorite toy.

3. WE USED SILICON FOR THOUSANDS OF YEARS WITHOUT KNOWING ITS ELEMENTAL NATURE.

Silica is the main ingredient of glass, which humans have been making at least since the Egyptians fashioned beads from the material in 2500 BCE. In China, the Qin and Han dynasties used purple and blue pigments made of barium copper silicates for various decorations, including parts of the famous terra-cotta army.

It took many centuries before people realized the substance could be further separated into two different elements—oxygen and silicon. In the late 1700s, French chemist Antoine Lavoisier noticed that certain materials classified as “earth” substances (which were dry and cold) sometimes behaved like metals (hard, dense, and resistant to being stretched, among other qualities). Silica was one of them. Perhaps, Lavoisier mused, some of the earths were really molecules of oxygen and a yet-undiscovered, metal-like element.

At the time, chemists didn’t know how to remove the oxygen atoms, which form strong bonds with the silicon atoms. That changed in the 1820s, when a Swedish chemist named Jons Berzelius finally managed to obtain silicon in his lab by purifying it from a silicon-containing compound. (Which one, and how he did it, isn't clear.) Berzelius's breakthrough came too late for Lavoisier, who had died in 1794, to see his speculations be proven true.

4. SILICA IS THE MOST COMMON FORM OF SILICON.

Also known as silicon dioxide, this molecule is composed of one silicon atom and two oxygen atoms (SiO2). Most of what we call silicon is actually silica, found in both minerals and plants. Many plants create unique microscopic structures called phytoliths using silica they take up from the soil. Scientists aren't sure why: They might offer protection against microscopic harm or provide structural support, or maybe they're just a way for a plant to use up extra silica.

Phytoliths stick around long after a plant decays, which can illuminate the deep history of an area—whether it used to be a forest or grassland, for instance, or how people used the landscape. Dan Cabanes, a phytolith expert and anthropologist at Rutgers University, has used phytoliths to understand how Neanderthals made a home in a cave in northern Spain, creating a sleeping area with grass bedding they used repeatedly. And because phytoliths survive burning, “we can study how they made fire or what type of food they were consuming,” Cabanes tells Mental Floss.

The picture isn’t always perfect, though, because sometimes two different plants make phytoliths of the same shape—and some plants don’t make them at all.

5. IT'S A KEY COMPONENT OF SOME BEAUTIFUL STONES …

iStock

Gorgeous gemstones like amethyst, onyx, and agate are all made of silica. In each rock, the silica molecules are arranged in repeating 3D geometries called crystal structures. Different arrangements, as well as small impurities in the rock, give each gemstone its unique appearance.

6. … AND THE DAZZLING BEAUTY OF DIATOMS.

Anatoly Mikhaltsov, Wikimedia Commons // CC BY-SA 4.0

Silica also forms the cell walls of diatoms, a type of algae found all over the world. Diatoms, which come in a mesmerizing variety of shapes, can live in both fresh and saltwater. When they die, their cell walls can accumulate into chalky deposits of "diatomaceous earth," which we use in all sorts of things, from cat litter to toothpaste.

7. SILICON IS VERY USEFUL IN TECH …

Silicon can act as a semiconductor—a material that neither conducts electricity perfectly nor insulates against it, but rather lies somewhere in between. This property is important in many parts of electronics, where you want some control over the flow of electricity. “What's beautiful about semiconductors is that you can tune their conductivity by adding impurities,” Eric Pop, a professor of electrical engineering at Stanford University, tells Mental Floss. Pure silicon is an insulator, but if you ‘dope’ it with tiny amounts of certain other elements, such as phosphorus or arsenic, it becomes better at conducting electricity.

Other materials, including germanium or gallium arsenide, are better semiconductors than silicon, but silicon is the most popular choice among electronics manufacturers (whose concentration south of San Francisco in the 1970s inspired the name "Silicon Valley"). It's cheap, it’s everywhere, and because it likes to oxidize so much, it can conveniently create its own insulating layer when exposed to air.

8. … BUT RESEARCHERS WANT TO FIND BETTER OPTIONS.

Engineers like Pop are looking for materials to replace silicon in our electronics to help keep up with the demand for faster computing. “Silicon is sort of like the Honda Civic of semiconductors,” Pop says. “It gets the job done, but it’s not very fast.” However, Pop thinks that even when pitted against superior materials, silicon won’t completely disappear, thanks to its low cost.

9. SILICON HOLDS UP MANY OF OUR BUILDINGS.

iStock

Many common building materials are based on silicon-containing substances. Clay minerals, which contain silicon, are used to make bricks, as well as Portland cement, which is then used as the binding agent in concrete.

10. AMERICANS LEFT A BIT OF SILICON ON THE MOON.

When Buzz Aldrin and Neil Armstrong became the first humans to walk on the Moon, in 1969, they left a few things on its surface besides their footprints. One was a small silicon disc, inscribed with messages from the leaders of 73 countries, from Afghanistan to Zambia. The disc is housed inside a protective aluminum case and is stashed in a small bag along with a few other items. Silicon was elected official message-bearer because it could endure the huge range of temperatures on the Moon. The disc nearly didn’t make it, though: Aldrin had forgotten all about the bag, tucked into a pocket of his space suit sleeve, and he was already on the ladder to the spacecraft when Armstrong reminded him about it. Aldrin tossed the pouch onto the Moon.