Print Friendly, PDF & Email
a mountain of gray limestone rock with green pine trees

Chalk cliff (made of calcium atoms) in Cottonwood Canyon, Pueblo, Colorado

What is calcium?

When a star is on the way to converting all of its carbon and oxygen atoms into iron, calcium is one kind of atom it makes along the way.

More about stars
And about atoms
All our chemistry articles

What’s in a calcium atom?

One atom of calcium has 20 protons and 20 electrons (and 20 neutrons). Calcium is a light kind of metal, not as strong as iron, though it is harder than lead.

More about metals

How did calcium get to Earth?

A man mixing concrete

After the star is done changing its atoms to iron, it explodes, shooting the calcium atoms out into a new nebula. Many of the calcium atoms in our nebula got made into part of the Earth. So many calcium atoms reached Earth, in fact, that calcium is the fifth most common element in the Earth’s crust.

What is a nebula?
And a supernova?
How old is the Earth?

hard yellow cheese - a good calcium source

A piece of cheese – lots of calcium!

Calcium in rocks

Most of the calcium on Earth is mixed with carbon to make molecules of calcium carbonate. That’s what sedimentary rocks like limestone and chalk are made out of. Then we burn limestone to make cement and concrete.

What is limestone?
And what’s marble?
Sedimentary rocks

Calcium in eggshells and bones

Cracked egg with yolk and white

Eggshells have a lot of calcium

But calcium is also one of the main atoms involved in making living creatures. Sponges and other animals make their hard structure out of calcium. All chordates make their bones and eggshells out of calcium.

More about eggs
And about bones

How do people get calcium?

People need calcium too: our bones are mostly made of calcium. That’s why it’s important to eat foods that have calcium in them. Some people drink milk or eat cheese or yogurt.

How to make yogurt
History of cheese
Where does tofu come from?

Others eat tofu, beans, almonds, and kale to get enough calcium.

What if you don’t get enough calcium?

Kids who don’t get enough calcium can get rickets, where your leg bones are weak and curved.

Learn by doing – an experiment with chalk
More about limestone
And about marble
How calcium makes eggshells

Bibliography and further information about atoms:

Chemistry home