Wait. Rocks are made of air?! 🪨

A mountain is a kind of frozen air.

Rocks that my kids gave me when they were younger. They used to love collecting rocks. I keep these near my desk.

I’m not sure why I was thinking about this recently. Maybe because we watched Project Hail Mary with the kids and one of the characters kinda looks like a rock.

I was wondering: what are rocks actually made of? Like what kinds of atoms?

So I looked it up, and I was surprised to find that the most abundant element in Earth’s crust isn’t silicon, iron, or aluminum.

It’s oxygen.

Wait. Rocks are made of air?!

By mass, the crust is about 46.6% oxygen and 27.7% silicon, followed by the usual suspects: aluminum, iron, calcium, sodium, potassium, magnesium, etc. By number of atoms, oxygen is about 60.5%.

Of course, the same element can be very different depending on what else it’s bonded to. Table salt is made from sodium and chlorine, two things you wouldn’t want to sprinkle on your food in their elemental form 🧂😵☠️

So it’s oxygen, but chemically locked into silicates, oxides, and carbonates. Quartz, for example, is SiO₂. By mass, it’s 53.3% oxygen, and by number of atoms, it’s 66.7% oxygen.

The atomic structure of quartz.

A lot of ordinary rocks are basically rigid three-dimensional scaffolding of oxygen atoms, with silicon, aluminum, iron, magnesium, and other atoms mixed in.

A rock is kind of frozen air. Not literally, the chemistry is different, but the summer breeze and a huge mountain are cousins, in a way 🤔

🧭 This first appeared in Edition 652 of Liberty’s Highlights. New here? I made a page for that: Start Here.